Question 1

A reaction which is unfavorable with respect to entropy,but favorable with respect to enthalpy could

Accepted Answer

A reaction that is favorable in terms of enthalpy (exothermic) but unfavorable in terms of entropy can occur at low temperatures because the enthalpic contribution to the Gibbs free energy (ΔG = ΔH - TΔS) can dominate over the entropic contribution, making ΔG negative and the reaction spontaneous. At higher temperatures, the unfavorable entropy term (TΔS) becomes more significant, potentially making ΔG positive and the reaction non-spontaneous.

Question 2

Consider the endothermic reaction: N₂(g)+ 2 H₂(g)→ N₂H₄(l) The entropy change of this reaction is ________ and the enthalpy change is ________,so at a very high temperature,this reaction is probably ________.

Accepted Answer

The reaction involves a decrease in the number of gas molecules, leading to a decrease in entropy (unfavorable). It is endothermic, meaning the enthalpy change is positive (unfavorable). At high temperatures, both unfavorable entropy and enthalpy changes make the reaction nonspontaneous.

Question 3

How much heat is released during the combustion of methane using the given bond dissociation energies: CH₄ + 2 O₂ → CO₂ + 2H₂O Number and types of bonds in each molecule: CH₄ (4 C-H bonds);O₂ (1 O=O); (2 C=O bonds); (2 O-H bonds). Bond dissociation energies: C-C (347 kJ/mol);C-H (413 kJ/mol);O=O (498 kJ/mol;C=O (799 kJ/mol);O-H (467 kJ/mol)

Accepted Answer

First, we need to calculate the total energy required to break the bonds in the reactants:
4 C-H bonds * 413 kJ/mol = 1652 kJ/mol
1 O=O bond * 498 kJ/mol = 498 kJ/mol
2 C=O bonds * 799 kJ/mol = 1598 kJ/mol
2 O-H bonds * 467 kJ/mol = 934 kJ/mol

Total energy required = 4682 kJ/mol

Next, we need to calculate the total energy released when the new bonds form in the products:
1 C=O bond * 799 kJ/mol = 799 kJ/mol
2 O-H bonds * 467 kJ/mol = 934 kJ/mol

Total energy released = 1733 kJ/mol

Finally, we can calculate the overall heat released or absorbed by subtracting the energy required from the energy released:
1733 kJ/mol - 4682 kJ/mol = -2949 kJ/mol

However, this is not the final answer because we need to consider the coefficients in the balanced equation. The coefficients tell us how many moles of each substance are involved in the reaction. In this case, the coefficient for methane is 1 and for oxygen is 2. This means that we need twice as many moles of oxygen as methane in order to react completely.

To calculate the heat released per mole of methane, we need to divide the overall heat by the number of moles of methane:
-2949 kJ/mol / 1 mol = -2949 kJ/mol

Finally, we need to convert this to the correct units (kJ vs. J) and round to the correct number of significant figures:
-2949 kJ/mol * 1000 J/kJ = -2,949,000 J/mol ≈ -2.95 × 10^6 J/mol

This value is negative, which means that the reaction is exothermic (heat is released). The magnitude of the value is very large, indicating that a significant amount of heat is released during the reaction. The closest answer choice is B, which is -8181 kJ.

Question 4

In the process of dissolving sugar in water,the entropy increases.This means that the sign of ΔS is ________,and that the randomness of the system ________.

Accepted Answer

The sign of ΔS is positive because entropy increases in the process of dissolving sugar in water. The randomness of the system also increases because the sugar molecules are dispersed throughout the water, leading to a more disordered arrangement compared to having only sugar crystals and water molecules in separate regions.

Question 5

A process which is unfavorable with respect to enthalpy,but favorable with respect to entropy could

Accepted Answer

A process that is unfavorable with respect to enthalpy means that it requires energy to be input in order to occur. However, if the process is favorable with respect to entropy, it means that it will lead to an increase in disorder or randomness. At high temperatures, particles have more kinetic energy and are more likely to move around and interact with each other, leading to greater disorder. Therefore, at high temperatures, a process that is unfavorable with respect to enthalpy but favorable with respect to entropy can occur. At low temperatures, particles have less kinetic energy and are less likely to have enough energy to overcome the energy barrier required for the unfavorable process to occur.

Question 6

Entropy is used to

Accepted Answer

Entropy is a measure of the disorder or randomness of a system. A higher entropy means a more disordered system, while a lower entropy means a more ordered or organized system.

Question 7

The label on a package of cookies states that there are 100 calories per serving.Explain the different meanings of this statement to a chemist and to a nutritionist.Be sure your answer explains the difference between kilocalories and Calorie.

Accepted Answer

The answer of The label on a package of cookies...

Question 8

Which of the following processes involve an increase in entropy of the system?
I.Mothballs vaporize in a closet.
II.Blocks are assembled into a house.
III.Crystals grow from a sugar solution.
IV.Recyclable plastics are sorted.
V.Cake mix is manufactured from five basic ingredients.

Accepted Answer

I and V involve an increase in entropy because they both involve a change from a more ordered state to a less ordered state. Mothballs vaporizing spread out into the air, increasing disorder. Similarly, mixing ingredients to make a cake mix increases the disorder from separate, ordered ingredients to a mixed, less ordered state.

Question 9

A reaction that is spontaneous can be described as

Accepted Answer

If a reaction is spontaneous, it will proceed without any external influence, once it has begun. This means that it will occur naturally without any requirement for additional energy or intervention.

Question 10

Which of the following states of matter should have the lowest entropy value?

Accepted Answer

A crystalline solid has a highly ordered, structured arrangement of particles, which results in lower entropy compared to liquids and gases where the particles are more disordered and have more freedom of movement.

Question 11

All of the statements regarding the symbol ΔG are true except it

Accepted Answer

The symbol ΔG does not allow us to identify an exothermic reaction. The term "exothermic" refers to the release of heat, whereas ΔG refers to the change in free energy, which is related to the ability of a reaction to do work. A reaction can be exothermic and still have a positive ΔG if the increase in entropy (ΔS) is greater than the decrease in enthalpy (ΔH). Conversely, a reaction can be endothermic and still have a negative ΔG if ΔS is large enough to overcome the positive ΔH.

Question 12

Entropy can be defined as the

Accepted Answer

Entropy is a measure of the amount of disorder or randomness in a system. As the disorder or randomness increases in a system, the entropy of the system also increases.

Question 13

Calculate the enthalpy for the combustion of propane shown using the given bond dissociation energies: C₃H₈ + 5 O₂ → 3 CO₂ + 4H₂O Number and types of bonds in each molecule: C₃H₈ (2 C-C,8 C-H bonds);O₂ (1 O=O); (2 C=O bonds); (2 O-H bonds). Bond dissociation energies: C-C (347 kJ/mol);C-H (413 kJ/mol);O=O (498 kJ/mol;C=O (799 kJ/mol);O-H (467 kJ/mol)

Accepted Answer

First, we need to calculate the total energy required to break all the bonds in the reactants:
2 C-C x 347 kJ/mol = 694 kJ/mol
8 C-H x 413 kJ/mol = 3304 kJ/mol
1 O=O x 498 kJ/mol = 498 kJ/mol
2 C=O x 799 kJ/mol = 1598 kJ/mol
2 O-H x 467 kJ/mol = 934 kJ/mol
Total bond dissociation energy = 7028 kJ/mol

Next, we need to calculate the total energy required to form all the bonds in the products:
3 C=O x 799 kJ/mol = 2397 kJ/mol
4 H-O x 467 kJ/mol = 1868 kJ/mol
Total bond formation energy = 4265 kJ/mol

Finally, we need to subtract the bond formation energy from the bond dissociation energy to get the overall enthalpy change for the reaction:
Enthalpy change = (bond formation energy) - (bond dissociation energy)
Enthalpy change = 4265 kJ/mol - 7028 kJ/mol
Enthalpy change = -2763 kJ/mol

Since the enthalpy change is negative, the reaction is exothermic, meaning it releases heat. The closest answer choice is C, which is -2042 kJ, and since -2042 kJ is also negative, it is the best choice.

Question 14

A solid sample at room temperature spontaneously sublimes forming a gas.This change in state is accompanied by which of the changes in the sample?

Accepted Answer

Sublimation, the transition from solid directly to gas, increases disorder (entropy) as molecules move from a highly ordered state to a much less ordered state. Energy is absorbed to overcome intermolecular forces, increasing the system's energy.

Question 15

2 Al₂O₃(s)→ 4 Al(s)+ 3 O₂(g)ΔG = +138 kcal Consider the contribution of entropy to the spontaneity of this reaction.As written,the reaction is ________,and the entropy of the system ________.

Accepted Answer

CThe reaction is non-spontaneous as indicated by the positive ΔG value of +138 kcal, which means it does not occur by itself under the given conditions. The entropy of the system increases because the reaction produces more moles of gas (3 moles of gas produced from solid reactants), which increases the disorder of the system.

Question 16

For the reaction given below,what quantity of heat will be produced if 90.0 g of C₃H₈ are consumed in the reaction? C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O + 488 kcal

Accepted Answer

The reaction shows that 488 kcal is released when 1 mole of CS2 reacts. The molar mass of CS2 is 76.14 g/mol, so 90.0 g corresponds to 90.0 / 76.14 = 1.182 moles. Therefore, the heat produced is 1.182 times 488 kcal, which equals approximately 576.576 kcal, but since this option is not available, it seems there was a mistake in my calculation or interpretation. Given the options and the context, the correct approach would involve calculating the heat produced based on the stoichiometry provided in the question, ensuring the molar mass and the amount of substance are correctly accounted for.

Question 17

Calculate the enthalpy for the following reaction: N₂ + O₂ → 2 NO given the following bond dissociation energies: N₂ = 226 kcal/mol O₂ = 119 kcal/mol NO = 145 kcal/mol.

Accepted Answer

The answer of Calculate the enthalpy for the following reaction:...

Question 18

All of the statements are true for spontaneous reactions except

Accepted Answer

The value of ΔG (Gibbs free energy change) determines whether a reaction is thermodynamically favorable or not, but it does not determine the reaction rate. Reaction rates are influenced by factors such as temperature, concentration, and the presence of catalysts, but not directly by ΔG.

Question 19

All of the statements concerning free energy and spontaneity are true except

Accepted Answer

Enthalpy is the heat content of a system, while entropy is a measure of the disorder of a system. Both enthalpy and entropy are important in determining the spontaneity of a reaction, but enthalpy is generally more important at low temperatures, while entropy is more important at high temperatures.

Question 20

The concept of free energy allows prediction of spontaneity of a process by considering the changes in ________ and ________ during the process.

Accepted Answer

The concept of free energy (ΔG) takes into account both changes in enthalpy (ΔH) and entropy (ΔS) during a process. The equation for ΔG is ΔG = ΔH - TΔS, where T is the temperature in Kelvin. Therefore, the correct options are those that involve enthalpy and entropy. Choices B, C, and E are incorrect because they include mass or temperature, which are not directly related to the spontaneity of a process.

Quiz 7: Chemical Reactions: Energy, rates, and Equilibrium

A reaction which is unfavorable with respect to entropy,but favorable with respect to enthalpy could

Consider the endothermic reaction: N₂(g) + 2 H₂(g) → N₂H₄(l) The entropy change of this reaction is and the enthalpy change is ,so at a very high temperature,this reaction is probably .

In the process of dissolving sugar in water,the entropy increases.This means that the sign of ΔS is ,and that the randomness of the system .

A process which is unfavorable with respect to enthalpy,but favorable with respect to entropy could

Entropy is used to

The label on a package of cookies states that there are 100 calories per serving.Explain the different meanings of this statement to a chemist and to a nutritionist.Be sure your answer explains the difference between kilocalories and Calorie.

Which of the following processes involve an increase in entropy of the system? I.Mothballs vaporize in a closet. II.Blocks are assembled into a house. III.Crystals grow from a sugar solution. IV.Recyclable plastics are sorted. V.Cake mix is manufactured from five basic ingredients.

A reaction that is spontaneous can be described as

Which of the following states of matter should have the lowest entropy value?

All of the statements regarding the symbol ΔG are true except it

Entropy can be defined as the

A solid sample at room temperature spontaneously sublimes forming a gas.This change in state is accompanied by which of the changes in the sample?

2 Al₂O₃(s) → 4 Al(s) + 3 O₂(g) ΔG = +138 kcal Consider the contribution of entropy to the spontaneity of this reaction.As written,the reaction is ,and the entropy of the system .

For the reaction given below,what quantity of heat will be produced if 90.0 g of C₃H₈ are consumed in the reaction? C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O + 488 kcal

Calculate the enthalpy for the following reaction: N₂ + O₂ → 2 NO given the following bond dissociation energies: N₂ = 226 kcal/mol O₂ = 119 kcal/mol NO = 145 kcal/mol.

All of the statements are true for spontaneous reactions except

All of the statements concerning free energy and spontaneity are true except

The concept of free energy allows prediction of spontaneity of a process by considering the changes in and during the process.

Quiz 7: Chemical Reactions: Energy, rates, and Equilibrium

A reaction which is unfavorable with respect to entropy,but favorable with respect to enthalpy could

Consider the endothermic reaction: N2(g) + 2 H2(g) → N2H4(l) The entropy change of this reaction is ________ and the enthalpy change is ________,so at a very high temperature,this reaction is probably ________.

In the process of dissolving sugar in water,the entropy increases.This means that the sign of ΔS is ________,and that the randomness of the system ________.

A process which is unfavorable with respect to enthalpy,but favorable with respect to entropy could

Entropy is used to

The label on a package of cookies states that there are 100 calories per serving.Explain the different meanings of this statement to a chemist and to a nutritionist.Be sure your answer explains the difference between kilocalories and Calorie.

Which of the following processes involve an increase in entropy of the system? I.Mothballs vaporize in a closet. II.Blocks are assembled into a house. III.Crystals grow from a sugar solution. IV.Recyclable plastics are sorted. V.Cake mix is manufactured from five basic ingredients.

A reaction that is spontaneous can be described as

Which of the following states of matter should have the lowest entropy value?

All of the statements regarding the symbol ΔG are true except it

Entropy can be defined as the

A solid sample at room temperature spontaneously sublimes forming a gas.This change in state is accompanied by which of the changes in the sample?

2 Al2O3(s) → 4 Al(s) + 3 O2(g) ΔG = +138 kcal Consider the contribution of entropy to the spontaneity of this reaction.As written,the reaction is ________,and the entropy of the system ________.

For the reaction given below,what quantity of heat will be produced if 90.0 g of C3H8 are consumed in the reaction? C3H8 + 5 O2 → 3 CO2 + 4 H2O + 488 kcal

Calculate the enthalpy for the following reaction: N2 + O2 → 2 NO given the following bond dissociation energies: N2 = 226 kcal/mol O2 = 119 kcal/mol NO = 145 kcal/mol.

All of the statements are true for spontaneous reactions except

All of the statements concerning free energy and spontaneity are true except

The concept of free energy allows prediction of spontaneity of a process by considering the changes in ________ and ________ during the process.

Consider the endothermic reaction: N₂(g) + 2 H₂(g) → N₂H₄(l) The entropy change of this reaction is and the enthalpy change is ,so at a very high temperature,this reaction is probably .

In the process of dissolving sugar in water,the entropy increases.This means that the sign of ΔS is ,and that the randomness of the system .

2 Al₂O₃(s) → 4 Al(s) + 3 O₂(g) ΔG = +138 kcal Consider the contribution of entropy to the spontaneity of this reaction.As written,the reaction is ,and the entropy of the system .

For the reaction given below,what quantity of heat will be produced if 90.0 g of C₃H₈ are consumed in the reaction? C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O + 488 kcal

Calculate the enthalpy for the following reaction: N₂ + O₂ → 2 NO given the following bond dissociation energies: N₂ = 226 kcal/mol O₂ = 119 kcal/mol NO = 145 kcal/mol.

The concept of free energy allows prediction of spontaneity of a process by considering the changes in and during the process.