Question 1

Which statement best describes the First Law of Thermodynamics as applied to chemical reactions?

Accepted Answer

Energy is conserved; it can be transferred between system and surroundings, but cannot be created or destroyed.

Question 2

A sample of gas expands against a constant external pressure. Which equation correctly expresses the work done by the system?

Accepted Answer

$$w = P 	imes \Delta V$$

Question 3

Which of the following is an example of an extensive property?

Accepted Answer

Enthalpy

Question 4

A chemical cold pack contains ammonium nitrate that dissolves in water, causing the pack to feel cold. What type of process is this?

Accepted Answer

Endothermic, because heat is absorbed from the surroundings.

Question 5

Which of the following statements about state functions is correct?

Accepted Answer

State functions depend only on the initial and final states, not the path taken.

Question 6

Calculate the amount of heat required to raise the temperature of 500.0 g of water from 25.0°C to 100.0°C. (Specific heat of water $$c = 4.18 \ \mathrm{J/g$$^{\circ}$$C})$$

Accepted Answer

$$q = 156,750 \ \mathrm{J}$$

Question 7

Which calorimeter is used to measure the heat of combustion at constant volume?

Accepted Answer

Bomb calorimeter

Question 8

A reaction has $$q = +120 \ \mathrm{J}$$ and $$w = -75 \ \mathrm{J}. $$What is the change in internal energy $$\Delta E$$?

Accepted Answer

$$\Delta E = 45 \ \mathrm{J}$$

Question 9

Which of the following best describes the sign conventions for heat ($$q) $$and work ($$w) in $$thermodynamics?

Accepted Answer

$$q \u003e 0$$ when heat is absorbed by the system; $$w \u003c 0$$ when work is done by the system.

Question 10

Which equation is used to calculate the heat transferred to a substance when its temperature changes?

Accepted Answer

$$q = m c \Delta T$$

Question 11

A 15.0 g sample of ethyl alcohol is heated from 22.70°C to 26.20°C by absorbing 129 J of heat. What is the specific heat capacity of ethyl alcohol?

Accepted Answer

$$c = 2.44 \ \mathrm{J/g$$^{\circ}$$C}$$

Question 12

Which of the following is true about the standard enthalpy of formation ($$\Delta H_f^\circ$$)?

Accepted Answer

It is the enthalpy change for forming one mole of a compound from its elements in their standard states.

Question 13

Which statement about Hess's Law is correct?

Accepted Answer

The enthalpy change for a reaction is independent of the path taken and can be calculated by summing enthalpy changes of individual steps.

Question 14

A 250.0 g sample of aluminum ($$c = 0.903 \ \mathrm{J/g$$^{\circ}$$C}) at 100.0$$°C is placed in a calorimeter containing 100.0 g of water at 25.0°C. What is the final temperature, assuming no heat loss to the surroundings? (Specific heat of water $$c = 4.18 \ \mathrm{J/g$$^{\circ}$$C})$$

Accepted Answer

$$T_f \approx 39.6$$^{\circ}$$C$$

Question 15

Which of the following reactions is exothermic?

Accepted Answer

Combustion of octane in air

Question 16

Which property does NOT depend on the amount of substance present?

Accepted Answer

Specific heat capacity

Question 17

Given the reaction: $$2 \mathrm{CO}(g) + \mathrm{O}_2(g) \rightarrow 2 \mathrm{CO}_2(g)$$, and the standard enthalpy of formation values $$\Delta H_f^\circ(\mathrm{CO}_2) = -393.5 \ \mathrm{kJ/mol}$$ and $$\Delta H_f^\circ(\mathrm{CO}) = -110.5 \ \mathrm{kJ/mol}$$, what is the enthalpy change for the reaction?

Accepted Answer

$$\Delta H^\circ = -566.0 \ \mathrm{kJ}$$

Question 18

Which of the following best describes the difference between system and surroundings in thermochemistry?

Accepted Answer

The system is the part of the universe under study; the surroundings are everything else.

Question 19

Which of the following is the correct mathematical statement for the First Law of Thermodynamics?

Accepted Answer

$$\Delta E = q + w$$

Thermochemistry and Energy Changes in Chemical Reactions

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