Chemistry High School

Which of the following processes is exothermic?
a. The reaction associated with DH°f for an ionic compound the ionization of a lithium atom.
b. The sublimation of dry ice (CO2(s))
c. The breaking of a Cl-Cl bond
d. All of the above processes are exothermic

Answers

Answer 1

Answer:

a. The reaction associated with DHºf for an ionic compound

Explanation:

An exothermic process is a process that loses heat for the surroundings, so the temperature of the system must decrease, and ΔH must be negative.

DHºf or ΔHºf of an ionic compound is always negative because the final energy is always lower than the initial. It happens because of the stability of the bond, the system wants a lower energy state to be stable.

The ionization of a lithium atom occurs with the gain of energy, which is given to the electron, so it may give off the atom. So it's an endothermic process.

To change the state of a solid to a gas (sublimation), the compound must gain heat, its temperature must increase, so it's always an endothermic process.

To break a covalent bond it's necessary the gain of energy, so it's an endothermic process.

Answer 2

Answer:A

Explanation:

The enthalpy change of formation for an ionic compound is calculated from the Born-Haber cycle. Using the Hess law of constant heat summation. The result is always negative (exothermic) because energy is given out when the new lattice is formed.

Related Questions

Which components of the atom have no charge? None of the components have charges. neutrons electrons protons

Answers

Answer:

The answer to your question is: neutrons

Explanation:

None of the components have charges. This is incorrect because the atoms is composed by three particles, neutrons, electrons and protons, and the characteristic of an atom is that its particles at least some are charged.

neutrons: are particles located in the nucleus and they diminish the repulsion forces among the protons. They don't have any charge

electrons : they are located in the shells are are negative charged.

protons: they are located in the nucleus and are positive charged.

Answer:

neutrons

Explanation:

The mass number of an atom is 15, and its atomic number is 7. The atom probably has... 8 neutrons in the nucleus. about as much mass in electrons as in protons. at least 15 electrons. 7 units of negative charge in the nucleus. 7 electrons in the nucleus.

Answers

Answer: Option (a) is the correct answer.

Explanation:

Atomic number is the sum of only total number of protons present in an element. Whereas mass number is the sum of total number of both protons and neutrons present in an element.

For example, given atom has mass number as 15 and its atomic number is 7.

Therefore, number of neutrons present in it will be calculated as follows.

                    Mass number = no. of protons + no. of neutrons

                         15 = 7 + no. of neutrons

                    no. of neutrons = 15 - 7

                                               = 8

Thus, we can conclude that the given atom contains 8 neutrons in the nucleus.

Identify the oxidation number of carbon in the compound lithium carbonate.

Answers

Answer:

The answer to your question is: +4

Explanation:

Oxidation number of carbon in Li₂CO₃

To know the oxidation number of Carbon, first find the oxidation number of Li and Oxygen.

Li is located in group IA in the periodic table, and all the elements that belong to this group have an oxidation number of +1.

O is located in group VIA in the periodic table, all the elements of this group have an oxidation number of -2.

Also, consider that the sum of the oxidation numbers in a neutral molecule equals zero.

Then

              Lithium = +1 x 2 = +2

              Oxygen = -2 x 3 = -6

            +2 + Carbon oxidation number - 6 = 0

             Carbon oxidation number = 6 -2

             Carbon oxidation number = 4

                                       

The oxidation number of carbon in lithium carbonate is +4.

Given:

The compound - lithium carbonate  

To find :

The oxidation number of carbon in the given compound.

Solution:

The formula of lithium carbonate = [tex]Li_2CO_3[/tex]

Number of lithium atoms = 2Number of carbon atoms = 1Number of oxygen atoms = 2

Let the oxidation number of carbon be x.

The oxidation number of lithium is = +1

The oxidation number of oxygen = -2

The overall charge on the compound's molecule = 0

[tex]2\times (+1)+x+3\times (-2)=0\\\\+2+x-6=0\\\\x=+6-2=+4[/tex]

The oxidation number of carbon in lithium carbonate is +4.

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Which characteristic is found in liquids and gases? A. Has a fixed volume B. Particles stay in a fixed position C. No particle movement D. Takes the shape of the container

Answers

Answer:

The answer to your question is letter D.

Explanation:

A. Has a fixed volume This is not the right answer, liquids and gases take the shape of the container in which they are.

B. Particles stay in a fixed position This answer is wrong, this characteristic is  of solids but not of liquids and gases.

C. No particle movement This characteristic is also of solids, in liquids and gases the particles can move.

D. Takes the shape of the container. This is the right answer, liquids and gases take the shape of the container.

Answer:

D :)

Explanation:

Which equation using element symbols correctly describes the reaction: "Two molecules of sodium hydroxide plus one molecule of sulfuric acid reacts to form one molecule of sodium sulfate and 2 molecules of water?"
A. 2NaOH+H2SO4→Na2SO4+2H2O
B. 2NaOH+H2O→Na2SO4+2H2SO4
C. Na2SO4+H2SO4→NaOH+H2O
D. NaOH+H2SO4→Na2SO4+H2O

Answers

Final answer:

The correct equation for the reaction between two molecules of sodium hydroxide and one molecule of sulfuric acid is 2NaOH+H2SO4→Na2SO4+2H2O.

Explanation:

The equation that correctly describes the reaction where two molecules of sodium hydroxide react with one molecule of sulfuric acid to form one molecule of sodium sulfate and two molecules of water is: 2NaOH+H2SO4→Na2SO4+2H2O. This equation illustrates a neutralization reaction whereby sulfuric acid (a strong acid) reacts with sodium hydroxide (a strong base) to produce sodium sulfate, a salt, along with water. This is an example of a reaction with a diacid, where two moles of the base are required to fully neutralize one mole of the diacid, resulting in a salt and water as the products.

Scientists infer that early North American humans hunted the mastodon. Carbon-14 dating of the rib bone indicates that 2.4 half-lives have passed since the mastodon was killed. Approximately how many years ago did the mastodon die?

Answers

Answer:

d

Explanation:

Final answer:

The mastodon was estimated to have died around 13,752 years ago, as deduced using Carbon-14 dating. This period corresponds to when early North American humans likely hunted large games, including woolly mammoths using group cooperation and advanced tools.

Explanation:

Understanding the life and death of a mastodon involves knowing the process of Carbon-14 dating and using this method to estimate the time-frame of the mastodon's demise. Carbon-14 undergoes radioactive decay and has a half-life of approximately 5730 years. In this problem, it is stated that 2.4 half-lives have passed since the mastodon was killed. Therefore, by multiplying the half-life of Carbon-14 (5730 years) by the number of half-lives that have passed (2.4), we can estimate that the mastodon died around 13,752 years ago.

This timescale fits into the period when early North American humans were known to have hunted large game, such as the woolly mammoths. Both archaeological evidence and cave paintings suggest coordinated hunting efforts with the use of sophisticated tools. The simultaneous occurrence of human migration, climate changes, and habitat reduction has been detected in this time frame, adding to the plausibility of human hunting leading to the extinction of these large animals.

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If a lab requires each a lab group (3 students) to have 25 ml of a solution and it takes 15 grams of AgNO₃ cuprous nitrate, to make 1 liter of solution, how many grams are needed to make enough solution?

Answers

Answer:

0.375 grams are needed to make 25 mL solution.

Explanation:

Mass of [tex]AgNO_3[/tex] cuprous nitrate required to make 1 l of solution = 15 g.

1 L = 1000 mL

Mass of [tex]AgNO_3[/tex] cuprous nitrate required to make 1000 mL of solution = 15 g

Mass of [tex]AgNO_3[/tex] cuprous nitrate required to make 1 mL of solution:

[tex]=\frac{15}{1000} g[/tex]

Mass of [tex]AgNO_3[/tex] cuprous nitrate required to make 25 mL of solution:

[tex]=\frac{15}{1000} \times 25 g=0.375 g[/tex]

0.375 grams are needed to make 25 mL solution.

A 75 gram bar of gold is cut into three equal pieces. How does the density of each piece compare to the density of the original bar?


1. Each piece is 1/3 the density of the original bar

2. Each piece is the same as the density of the original bar

Answers

Answer:

You should know that density is the relation between, mass and volume as it is described in this equation: d = m/v. As the mass doesn't change in each piece, you will see that volume is less than the original, that's why each piece is 1/3 the density of the original bar or, you can also see, that you have increase by 3, the density original.

Explanation:

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