wrapping a hot dish of food in shiny aluminium foil seems to keep the dish warm longer than wrapping it in clear plastic film . aluminium is much better conductor of heat than plastics , so why does it impede the flow of heat so well?

Answers

Answer 1

There are three different mechanisms for heat to transfer. Let's take a look at them to see if any of them explain the cause.

1. Conduction - This is the transfer of heat from one object to another via physical contact. And in the question, aluminium is a far better conductor of heat than plastic, so aluminum would transfer heat faster via conduction than plastic. So the cause for the observed phenomena has to be one of the other 2 mechanisms.

2. Convection - This mechanism relies upon the fact that for fluids (both gasses and liquids) change their volume and therefore their density with changes in temperature. This means that you can have a fluid get warmed up by something that's hot, expand to decrease it's density and then get pushed away from the warm surface by colder, denser fluid. The warmed fluid then gets cooled off when it contacts a colder surface, it's density increases, and then flows back replacing the newly warmed fluid. For both aluminum and plastic, there is likely to be equivalent convection effects in the air gap between the hot food and the substance being used to cover the food. And once again, since aluminum is a better conductor of heat, it would be more effective in cooling the warmed air, making convection work faster. So this mechanism doesn't work either. So let's look at the 3rd method of transferring heat.

3. Radiation - This is the process by which heat is radiated out from a warmer body in all directions via photons traveling through either vacuum or a transparent medium. An example would be the heat you feel from an electric stove. In this case, the photons carrying energy will go right through the clear plastic wrap unimpeded, while they would be reflected back to the food with the aluminum foil. So of the 3 mechanisms, the aluminum foil impedes the flow of heat via radiation far better than the clear plastic film. And in fact, it does that so much better than even with the disadvantage the foil has via conduction, it's more than out weighed by the better performance against radiation.

Related Questions

Which of the following is NOT an assumption of the kinetic theory of gases?
A)Gas particles are in constant random motion.
B)The volume of individual gas particles is zero.
C)The particles in a gas are attracted to each other.
D)Gas particles collide without losing energy.

Answers

Which of the following is NOT an assumption of the kinetic theory of gases?
B)The volume of individual gas particles is zero.
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c) The particles in a gas are attracted to each other

How do most vertebrates reproduce—sexually or asexually? What are gametes? How is an embryo produced?

I NEED THE ANSWER QUICK

Answers

1) Sexually
2) A mature haploid male germ cell that is able to unite with another of the opposite sex in sexual reproduction to form a zygote.
3) In a placental mammal, an ovum Is fertilized in a fallopian tube through which it travels into the uterus.

I am studying for ACS and have trouble understanding how to rank molecules in decreasing or increasing solubility in water...

I know the rules of which molecules are insoluable...But how do you rank them in which is least or most soluble.

The question in the acs included
In which set are the substances arranged in order of decreasing solubility in water?

(A) Al(OH)3 > Mg(OH)2 > NaOH

(B) BaSO4 > CaSO4 > MgSO4

(C) CaCO3 > NaHCO3 > Na2CO3

(D) AgCl > AgBr > AgI

Answers

The set AgCl > AgBr > AgI are arranged in order of decreasing solubility in water. In order to get the solubility, it is measured in grams per 100 g of solvent – g/100 g – or number of moles per 1 L of the solution.

Sucrose is another name for table sugar. Sucrose is a compound made from the elements carbon, hydrogen, and oxygen. Which statement best describes the properties of sucrose?

Answers

Final answer:

Sucrose is a disaccharide compound of glucose and fructose and forms a homogeneous solution when dissolved in water. The physical and chemical properties of sucrose are quite different from its constituent elements in their individual states.

Explanation:

Sucrose, also known as table sugar, is a compound made of the elements carbon, hydrogen, and oxygen. Structurally, it's a disaccharide, meaning it consists of two sugar units; in this case glucose and fructose. Sucrose has covalent bonds and is a crystalline solid at room temperature. When dissolved in water, it forms a homogeneous solution where its molecules are uniformly distributed among the water molecules. These are some of the key properties of sucrose.

It's important to note that the properties of the sucrose molecule vastly differ from the properties of its constituent elements when in their free, or uncombined, state. Carbon, for instance, is a black solid and hydrogen and oxygen are colorless gases when uncombined, but when they chemically combine, they form the white, crystalline solid that is sucrose.

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1.
Which best describes the shape of myoglobin, which in many ways is a typical protein?

a complex three-dimensional shape formed from many twisted helixes

a cylindrical shape that forms from a single twisted helix

a straight chain, like beads on a straight piece of string

a highly-branched chain, much like the branches of a maple tree

Answers

Myoglobin, like most proteins, has a complex three dimensional structure that is formed from many twisted helices. There are more than one helix, and it does not look like beads on a straight piece of string. It is not branched.

EASY AND IMPORTANT What do you think is the most challenging aspect of using a microscope? What are the advantages and disadvantages of using a microscope to look at trace evidence?

Answers

The most challenging aspect is focusing the microscope.

Microscopes enables us to view objects that cannot be seen with the human eye alone.

A disadvantage is that not all types of evidence can be clearly seen.

What is a microscope?

A microscope is an instrument that is used to view tiny and microscopic objects.

In using a microscope, the most challenging aspect is focusing the microscope.

An advantage of microscopes is that they enable us to view objects that cannot be seen with the human eye alone.

A disadvantage though is that not all evidence can be clearly seen.

In conclusion, a microscope helps one to view trace and tiny objects.

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What is the mass, in grams, of 7.20×1020 molecules of caffeine, c8h10n4o2?

Answers

To determine the mass, you need to know the molecular weight of the c8h10n4o2 . The molecular weight of c8h10n4o2 would be: 8*12 + 10*1 + 4*14 + 2*16= 194g/mol.
To convert the number of molecules into moles, you need to divide it with 6.02 * 10^23. The calculation of the mass of c8h10n4o2 would be:
(7.20×10^20 molecules) /(6.02 * 10^23 molecule/mol) * 194g/mol= 232 * 10^-3 grams= 0.232 grams

Answer: 0.23 grams

Explanation:

According to avogadro's law, 1 mole of every substance weighs equal to its molecular mass and contains avogadro's number [tex]6.023\times 10^{23}[/tex] of particles.

To calculate the number of moles, we use the equation:

[tex]\text{Number of moles}=\frac{\text{Given molecules}}{\text{Avogadro's number}}=\frac{7.20\times 10^{20}}{6.023\times 10^{23}}=1.2\times 10^{-3}moles[/tex]

1 mole of caffeine [tex](C_8H_{10}N_4O_2)[/tex] weighs = 194 g

[tex]1.2\times 10^{-3}[/tex] moles of [tex](C_8H_{10}N_4O_2)[/tex] weigh = [tex]\frac{194}{1}\times 1.2\times 10^{-3}=0.23g[/tex]

Thus mass of caffeine [tex](C_8H_{10}N_4O_2)[/tex] is 0.23 grams.

Consider the balanced equation below.

What is the mole ratio of Fe3O4 to Fe?

1:3
1:4
3:1
4:3

Answers

Is the equation correctly balanced? Yes it is.

The mol ratio is the number in front of one chemical to the other.

There is a 3 in front of the Fe.
There is a 1 in front of the Fe3O4

Edit
What the original answer gave was the mole ratio of Fe to Fe3O4. It is actually the other way around. The answer should be 1:3 because it was asked as Fe3O4 to Fe.
The correct answer is A <<<<<<<< Correct Answer.

Answer:

1:3

Explanation:

Hope this helps :)

Describe how to make 1.50 liters of a 0.01 M ammonium chloride solution

Answers

Hello!

To know how many grams of Ammonium Chloride ( a solid) you'll need to make 1.50 L of a 0,01 M solution you'll need to use the definition of molar concentration (M=mol/L) in the following way:

[tex]1,50 L* \frac{0,01 mol NH_4Cl}{1L}* \frac{53,489gNH_4Cl}{1 mol NH_4Cl}=0,8023 g NH_4Cl [/tex]

So, you'll need to dissolve 0,8023 g of Ammonium Chloride in 1,5 L of water to make this solution.

Have a nice day!

What is the percent by mass of nahco3 in a solution containing 10 g of nahco3 dissolved in 400 ml of h2o?

Answers

Answer is: the percent by mass of NaHCO₃ is 2,43%.
m(NaHCO₃) = 10 g.
V(H₂O) = 400 ml.
d(H₂O) = 1 g/ml.
m(H₂O) = V(H₂O) · d(H₂O).
m(H₂O) = 400 ml · 1 g/ml.
m(H₂O) = 400 g.
m(solution) = m(H₂O) + m(NaHCO₃).
m(solution) = 400 g + 10 g.
m(solution) = 410 g.
ω(NaHCO₃) = 10 g ÷ 410 g · 100%.
ω(NaHCO₃) = 2,43 %

explain in terms of collision theory, how and why a reactions's rate changes as the reaction progresses

Answers

The rate of a chemical reaction is the speed with which the reactants are converted to products while the collision theory is used to explain why chemical reactions occur at different rates. It states that for a reaction to proceed, the reactants particles must collide and the more successful collisions there are per unit of time, the faster the reaction will be. As the reaction progresses, the products builds up in the system and the chance that the reactants will collide amongst themselves reduces as the product molecules begin to build up while the molecules of the reactants are deprived. therefore the rate of reaction changes.

Explanation:

According to collision theory, more is the number of collisions occurring between the combining substances more will be the rate of reaction.

Factors that affect rate of a reaction are as follows.

Temperature - Increase in temperature leads to increase in kinetic energy of particles due to which there occurs more number of collisions between them. As a result, rate of reaction will increase leading to increase in rapid formation of products.

Surface area - More is the surface area of a substance, less will be the interaction between solute and solvent particles. And, when there occurs decrease in surface area then interaction between solute and solvent particles increases. This leads to increase in rate of reaction.

Concentration of reactants - More is the concentration of reactant molecules more is the availability of molecule interaction. As a result, more number of collisions occur leading to increase in rate of a reaction.

How many times greater is the rate of effusion of molecular fluorine than that of molecular bromine at the same temperature and pressure?

Answers

According to Graham's law the rates of effusion of two gases are inversely proportional to the square roots of their molar masses at the same temperature and pressure: Effusion is used to describe the passage of a gas through a tiny office into an evacuated chamber.
Therefore;, R1/R2= √mm2/√mm1
The molecular mass of fluorine is 38 g and that of 160 g
Therefore; = √ (160/38)
= √ 4.211
= 2.051
Hence; the rate of effusion of molecular fluorine is 2.051 times than that of molecular bromine at the same temperature and pressure.

Answer: The rate of diffusion of fluorine is 2.05 times to that of bromine.

Explanation:

To calculate the rate of effusion of gas, we use Graham's Law.

This law states that the rate of effusion of gas is inversely proportional to the square root of the molar mass of the gas. The equation given by this law follows:

[tex]\text{Rate of diffusion}\propto \frac{1}{\sqrt{\text{Molar mass of the gas}}}[/tex]

Molar mass of bromine = 160 g/mol

Molar mass of fluorine = 38 g/mol

For the rate of effusion of bromine to fluorine we write the expression:

[tex]\frac{Rate_{F_2}}{Rate_{Br_2}}=\sqrt{\frac{M_{Br_2}}{M_{F_2}}}[/tex]

[tex]\frac{Rate_{F_2}}{Rate_{Br_2}}=\sqrt{\frac{160}{38}}=2.05[/tex]

Hence, the rate of diffusion of fluorine is 2.05 times to that of bromine.

What happens to an atom of fluorine (f) when it forms an ionic bond in which it has the same electron configuration as the noble gas neon?

Answers

It will gain one electron and become negatively charged

There are two types of chemical compound one is covalent compound and other is ionic compound, covalent compound formed by sharing of electron and ionic compound formed by complete transfer of electron. Therefore, one electron will be gained by fluorine during the reaction.

What is chemical Compound?

Chemical Compound is a combination of molecule, Molecule forms by combination of element and element forms by combination of atoms in fixed proportion.

The compound that is ionic in nature can be dissociated very easily in water. Since ionic compounds are polar in nature, they readily dissolve in water. When an atom of fluorine (f) when it forms an ionic bond in which it has the same electron configuration as the noble gas neon, one electron will be gained by fluorine to form negative charge anion.

Therefore, one electron will be gained by fluorine during the reaction.

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Nitrogen reacts with oxygen to form two compounds. compound a contains 2.8 g of nitrogen for each 1.6 g of oxygen. compound b contains 5.6 g of nitrogen for each 9.6 g of oxygen. what is the lowest whole-number mass ratio of nitrogen that combines with a given mass of oxygen?

Answers

Answer 1:
For compound A:
2.8 g of nitrogen for each 1.6 g of oxygen
Atomic weight of N = 14
Atomic weight of O = 16
Thus, number of moles of N = 2.8/14 = 0.2
and number of moles of O = 1.6/16 = 0.1

Thus, molar ratio of N and O in compound is 2:1.

Therefore, lowest whole-number mass ratio of nitrogen that combines with a given mass of oxygen is 2:1. And the compound formed is N2O.
.........................................................................................................................

Answer 2:
For compound B:
5.6 g of nitrogen for each 9.6 g of oxygen
Atomic weight of N = 14
Atomic weight of O = 16
Thus, number of moles of N = 5.6/14 = 0.4
and number of moles of O = 9.6/16 = 0.6

Thus, molar ratio of N and O in compound is 4:6 = 2:3.

Therefore, lowest whole-number mass ratio of nitrogen that combines with a given mass of oxygen is 2:3. And the compound formed is N2O3.

A 2.8 / 1.6 = ____
or
b 5.6 / 9.6 = ____

(obviously neither is a whole number)

We need to assume 100g of Nitrogen.

m (2.8 / 1.6) + n (5.6 / 9.6 ) = k(100)

where:

k = integer
m and n = grams of oxygen in each compound

Solution:

m = 100-n
(100 - n) (2.8 / 1.6) + n (5.6 / 9.6) = 100k
(100 - n) 1.75 + 0.583n = 100k
-1.166n = 100k -1.75
n = -85.71k + 150

if k=1,
n = 14.3
m =85.7

thus,

one has grams O =100, grams N = 14.3 * 2.8 / 1.6 + 85.7 * 5.6 /9.8 = 25.7 + 50g N or 75g N

the ration of N/O is 3/1 or rather 3:1

How many liters of fluorine gas, at 298 K and 0.98 atm, will react with 23.5 grams of potassium metal? Show all of the work used to solve this problem. 2K + F2 2KF

Answers

For the reaction 2 K + F2 --> 2 KF,
consider K atomic wt. = 39
23.5 g of K = 0.603 moles, hence following the molar ratio of the balanced equation, 0.603 moles of potassium will use 0.3015 moles of F2. (number of moles, n = 0.3015)

Now, following the ideal gas equation, PV = nRT
P = 0.98 atm
V = unknown
n = 0.3015 moles
R = 82.057 cm^3 atm K^-1mole^-1 (unit of R chosen to match the units of other parameters; see the reference below)
T = 298 K
Solving for V,
V = (nRT)/P = (0.3015 mol * 82.057 cm^3 atm K^-1 mol^-1 * 298 K)/(0.98 atm)
solve it to get 7517.6 cm^3 as the volume of F2 = 7.5176 liters of F2 gas is needed.

How many grams of sodium chloride are present in a 0.75 M solution with a volume of 500.0 milliliters? 0.38 grams 22 grams 0.75 grams 44 grams

Answers

I believe the answer is 0.38 grams.

Write the dissociation reaction and the corresponding ka equilibrium expression for hcn in water

Answers

Chemical reaction: HCN(aq) + H₂O(l) ⇄ CN⁻(aq) + H₃O⁺(aq).
Ka = [CN⁻] · [H₃O⁺] / [HCN].
[HCN] is equilibrium concentration of hydrocyanic acid.
hydrocyanic acid is weakly acidic and partially ionizes in water solution and give the cyanide anion (CN⁻).
The salts of the cyanide anion are called cyanides.

The dissociation reaction of HCN in water is HCN(aq) ↔ H⁺(aq) + CN⁻(aq).

Here is the balanced dissociation reaction for hydrocyanic acid (HCN) in water:

HCN(aq) ↔ H⁺(aq) + CN⁻(aq)

The equilibrium expression for the acid dissociation constant (Ka) for this reaction is given by:

Ka = [H⁺][CN⁻] / [HCN]

This expression shows that the equilibrium constant (Ka) for HCN dissociation is determined by the concentrations of the hydrogen ions (H⁺), the cyanide ions (CN⁻), and the undissociated hydrocyanic acid (HCN) in the solution.

Why is a spectrum for a given element unique for that element?

A. No element has more than two electrons in the first shell.
B. Each element has a unique arrangement of electrons.
C. Atoms of different elements have different masses.
D. Atomic nuclei contain no electrons.

Answers

Answer: B. Each element has a unique arrangement of electrons.

Explanation:

1) Since the number of electrons in neutral atoms is equal to the number of protons, and the number of protons are unique for each element, each element has a unique arrangement of electrons.

2) The spectrum of an element is the radiation emitted for the atoms of the element when the valence electrons are emitted and that depended on the electrons configuration.

Answer:

Explanation:

Which particles in an atom could demonstrate that opposite charges attract?

A.
a neutron and an electron
B.
two protons together
C.
a proton and a neutron
D.
a proton and an electron

Answers

D is true
protons are positively charged
and electrons have negative charge.
protons in the nucleus attract electrons around the nucleus

What is the maximum amount of kcl that can dissolve in 200 g of water? (the solubility of kcl is 34 g / 100 g h 2o at 20°c.) 6800 g 34 g 68 g 17 g?

Answers

the answer is 68 g
hope this helps!!

What was the total demand by all counties for water from the Sweetbriar River Basin in 1970? What is it projected to be in 2020?

Answers

Hey! 559 million kiloliters in 1970 and 1,476 million kiloliters in 2020.

559 million kiloliters in 1970 and 1,476 million kiloliters in 2020.

Hope this helpsssssssssssss!!!

An increase in temperature can disturb the liquid-vapor equilibrium
True
False

Answers

The answer is True.

when the temperature changes, it affects the equilibrium constant and that makes the equilibrium change.
because when the temperature changes that make the vapor pressure changes and make the equilibrium shifts.

What type of stress is caused by two plates sliding past one another?

Answers

That stress is compression. It forms Reverse Faults.

What is the [H+] of a solution with a pH of 6.6? Use a scientific calculator.

2.5 × 107

5.0 × 105

8.3 × 106

7.7 × 105

Answers

pH is a logarithmic scale as seen below:

pH = -log([H+])

Please note the negative sign in front of the log function. As concentration of H+ ions increases, the pH will decrease. If pH = 6.6, then:

pH = 6.6 = -log([H+])

You can multiple both sides by -1. Then, to get rid of the log function, set both sides of the equation equal to 10^ as shown below:

10^(-6.6) = [H+]

10^(-6.6) = 2.511x10^-7,

Considering the definition of pH, the concentration [H⁺] is 2.5 ×10⁻⁷ M.

Definition of pH

pH is the Hydrogen Potential. It is a measure of acidity or alkalinity that indicates the amount of hydrogen ions present in a solution or substance.

Mathematically, pH is calculated as the negative base 10 logarithm of the activity of hydrogen ions:

pH= - log [H⁺]

The numerical scale that measures the pH of substances includes the numbers from 0 to 14. The pH value 7 corresponds to neutral substances. Acidic substances are those with a pH lower than 7, while basic substances have a pH higher than 7.

Concentration [H⁺] of the solution

In this case, being pH= 6.6, you can replace this value in the definition of pH:

6.6 = -log [H⁺]

Solving:

[H⁺]= 10⁻⁶ ⁶ M

[H⁺]= 2.5 ×10⁻⁷ M

Finally, the concentration [H⁺] is 2.5 ×10⁻⁷ M.

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Use ksp=4.87×10−17 to calculate the solubility of iron (ii) hydroxide in pure water in grams per 100.0 ml of solution. g

Answers

The ksp = 4.87 × 10^-17
Therefore; 4.87 ×10^-17 = [Fe2+][OH-]^2 = (X)(2X)^2 = 4X^3
Hence;
4x^3 =4.87 × 10^-17
x = 2.30 × 10^-6 M
therefore the molarity is 2.3 ×10^-6 M
Thus;
The mass of Fe(OH)2 in 100 ml of water, will be given by:
= 2.30 × 10^-6 mol/L = 2.3 ×× 10^-5 mole/100 mL
= 89.86 g/mol × 2.3 × 10^-6 × 0.100 = 2.07 × 10^-5 g
= 2.07 × 10^-5 g
= 2.07 × 10^-5 g

The solubility product constant is the equilibrium constant of a substance in an aqueous solution. The solubility of iron (ii) hydroxide is [tex]2.07 \times 10^{-5}\;\rm g.[/tex]

What is Ksp?

Ksp is the solubility product constant, which is given as the product of the concentration of cation and anion dissociated in the aqueous solution.

Given,

Ksp = [tex]4.87 \times 10^{-17}[/tex]

Thus,

[tex]\begin{aligned}&= \rm [Fe^{2+}][OH^{-}]^{2} \\\\&= \rm (X)(2X)^{2} \\\\&= \rm 4X^{3}\end{aligned}[/tex]

The molarity can be calculated as:

[tex]\begin{aligned}\rm 4X^{3} =4.87 \times 10^{-17}\\\\\rm X= 2.30 \times 10^{-6}\;\rm M\end{aligned}[/tex]

The mass of iron (ii) hydroxide in 100 mL of water is calculated as:

[tex]\begin{aligned}2.30 \times 10^{-6} \;\rm mol/L &= 2.3 \times 10^{-5}\;\rm mole/100 mL\\\\&= 2.07 \times 10^{-5} \;\rm g\end{aligned}[/tex]

Therefore, the solubility of iron (ii) hydroxide is [tex]2.07 \times 10^{-5}\;\rm g.[/tex]

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4130 J of energy 52g water 10 c initial specific heat 4.18 J waht would the final temperature be

Answers

Heat energy = mass × specific heat capacity × change in temperature.
Heat energy = 4130 J, specific heat capacity of water = 4.18 J/g/C, the mass of water = 52 g, if final temperature is T
4130 = 52 × 4.18 ×(T-10)
4130 = 217.36 T - 2173.6
217.36 T = 6303.6
T = 29
Therefore the final temperature is 29 °C

Which changes are evidence of a chemical reaction? a beaker of water becomes hot to the touch upon?

Answers

Any change in temperature or new substance formed is evidence of a chemical reaction, this includes heat, gas or crystallization.

If the molecular mass of tetraoxosulphate(VI) acid is 98, calculate it's vapour density.

Answers

When the vapor density defined as the mass of a certain volume of the substance divided by the mass of the same volume of hydrogen.
So Vapor density = molar mass of gas/molar gas of hydrogen
when we have the molar mass of the tetraoxosulphate (VI) = 98 & and we have the molar mass of Hydrogen = 2 so by substitution.

∴ Vapor density = 98 / 2 = 49

1. A 10 g gold coin is heated from 25°C to 50°C (CAu is 0.13 J/g-°C). What is the H?
(Points : 1)
+32.5 J

25 J

+25 J

- 32.5 J

I know it is 32.5 J but is it negative or positive... I say it is negative, but I could be wrong...,

Answers

The correct answer is + 32.5 J because heat is absorbed here by copper not evolved also after calculation we will find the H value is positive, lets calculate it:
H = m C Δt where:
m = 10 g
C = 0.13 J/g.°C
Δ t = final temperature - initial temperature = 50 - 25 = + 25 °C
so H = 10 x 0.13 x (+25) = + 32.5 J

Answer:

+32.5 J

Explanation:

What is the ph of a buffer that is 0.6 m hf and 0.2 m naf ? the k a of hf is 6.8 × 10 −4 ?

Answers

Answer is: pH value for the buffer solution is 2,69.
c(HF) = 0,6 M.
c(NaF) = 0,2 M.
Ka(HF) = 6,8·10⁻⁴.

Henderson–Hasselbalch equation: pH = pKa + log(c(NaF)/c(HF)).

pH = -log(6,8·10⁻⁴) + log (0,2 M/0,6 M).

pH = 3,17 - 0,48.

pH = 2,69.

Answer:

pH of buffer is 2.69

Explanation:

According to Henderson-Hasselbalch equation for a buffer consists of an weak acid (HF) and it's conjugate base ([tex]F^{-}[/tex])-

[tex]pH=pK_{a}(HF)+log(\frac{C_{F^{-}}}{C_{HF}})[/tex]

Where C stands for concentration

[tex]pK_{a}=-log(K_{a})[/tex]

[tex]C_{F^{-}}[/tex] in 0.2 m NaF is 0.2 m

[tex]C_{HF}=0.6m[/tex]

So, [tex]pH=-log(6.8\times 10^{-4})+log(\frac{0.2}{0.6})=2.69[/tex]

Other Questions

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