Question 1

Which of the following best describes the law of conservation of energy?

Accepted Answer

The total energy in a system does not change; energy cannot be created or destroyed.

Question 2

A chemical reaction has a negative enthalpy change ($$\Delta H \u003c 0). $$Which of the following statements is true about this reaction?

Accepted Answer

The reaction is exothermic and releases heat.

Question 3

Which of the following best explains why increasing the temperature of a reaction generally increases its rate?

Accepted Answer

It increases the average kinetic energy of the molecules, leading to more effective collisions.

Question 4

Given the reaction: $$2CO(g) + O_2$(g) \rightleftharpoons 2CO_2(g)$$, what will happen if the concentration of $$CO_2(g$$)$$ is increased?

Accepted Answer

The concentrations of $$CO(g)$$ and $$O_2(g$$)$$ will increase as the reaction shifts to the left.

Question 5

Which of the following is true about catalysts in chemical reactions?

Accepted Answer

Catalysts lower the activation energy ($$E_a) $$without affecting the enthalpy change ($$\Delta H).$$

Question 6

For the reaction $$A_2(g$$) + $$B_2(g$$) \rightleftharpoons 2AB(g)$$, the equilibrium concentrations are $$[$$A_2$$] = 0.25\ M$$, $$[$$B_2$$] = 0.25\ M$$, and $$[AB] = 0.50\ M$$. What is the equilibrium constant K$?

Accepted Answer

$$K = \dfrac{[AB]^2}{[A_2$][B_2$]} = \dfrac{(0.50)^2$}{0.25 	imes 0.25} = 4.0$$

Question 7

Which of the following statements about bond dissociation energy is correct?

Accepted Answer

Bond dissociation energy is positive for breaking bonds because it is an endothermic process.

Question 8

A reaction has an activation energy ($$E_a) $$that is very high. What can you predict about the rate of this reaction at room temperature?

Accepted Answer

The reaction will be very slow because few molecules have enough energy to overcome the barrier.

Question 9

Which of the following best describes what happens to a system at equilibrium when the pressure is increased (assuming the reaction involves gases)?

Accepted Answer

The equilibrium shifts toward the side with fewer moles of gas.

Question 10

For the reaction $$N_2(g) + 3H_2(g$$) \rightleftharpoons 2NH_3(g)$$, what will happen if the temperature is increased, given that $$\Delta H = -22$$ kcal/mol (exothermic)?

Accepted Answer

The equilibrium will shift to the left, favoring $$N_2$$ and $$H_2.$$

Question 11

Which of the following is true about the magnitude of the equilibrium constant $$K$$?

Accepted Answer

If $$K \approx 1$$, both reactants and products are present in similar amounts.

Question 12

Which of the following best explains why enzymes are important in the human body?

Accepted Answer

They act as biological catalysts, speeding up specific reactions without being consumed.

Question 13

A reaction is endothermic. Which of the following statements is true?

Accepted Answer

The enthalpy change $$\Delta H is $$positive.

Question 14

Which of the following scenarios is an example of Le Chatelier’s Principle in action?

Accepted Answer

Adding more reactant to a system at equilibrium causes the system to shift to produce more product.

Question 15

Which of the following is the correct equilibrium constant expression for the reaction $$N_2(g$$) + $$O_2(g$$) \rightleftharpoons 2NO(g)$$?

Accepted Answer

$$K = \dfrac{[NO]^2}{[N_2$][O_2$]}$$

Question 16

Which of the following best describes the effect of a catalyst on a reaction energy diagram?

Accepted Answer

It lowers the activation energy ($$E_a) $$but does not change the enthalpy change ($$\Delta H).$$

Question 17

Which of the following is a correct statement about potential and kinetic energy in chemical systems?

Accepted Answer

Potential energy is stored in chemical bonds, and kinetic energy is the energy of motion.

Question 18

If a reaction at equilibrium is subjected to a decrease in pressure, what will happen if the reaction involves a decrease in the number of moles of gas from reactants to products?

Accepted Answer

The equilibrium will shift toward the reactants.

Question 19

Which of the following is the correct conversion between calories and joules?

Accepted Answer

$$1\ 	ext{cal} = 4.184\ 	ext{J}$$

Energy Changes, Reaction Rates, and Equilibrium – Chemistry Chapter 6 Study Notes

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