Question 1

Which of the following statements best describes the First Law of Thermodynamics?

Accepted Answer

The total energy of the universe is conserved; energy can change form but cannot be created or destroyed.

Question 2

A 250 g block of aluminum (specific heat $$C_s = 0.897 \ J/g\cdot ^\circ C) at$$ $$100^\circ C is $$placed in 500 g of water at $$20^\circ C. $$What is the final temperature of the system, assuming no heat is lost to the surroundings? (Specific heat of water $$C_s = 4.18 \ J/g\cdot ^\circ C)$$

Accepted Answer

$$T_f \approx 24^\circ C$$

Question 3

Which equation correctly relates the change in internal energy ($$\Delta E) of a $$system to heat ($$q) $$and work ($$w$$)?

Accepted Answer

$$\Delta E = q + w$$

Question 4

A chemical reaction in a cold pack absorbs heat from its surroundings. Which term best describes this process?

Accepted Answer

Endothermic

Question 5

Calculate the amount of heat required to raise the temperature of 150 g of water from $$25^\circ C to$$ $$75^\circ C$$. ($$C_s = 4.18 \ J/g\cdot ^\circ C)$$

Accepted Answer

$$q = 6270 \ J$$

Question 6

Which of the following is a state function?

Accepted Answer

Internal energy ($$E)$$

Question 7

A gas expands against a constant external pressure of $$2.0 \ atm$$ from $$5.0 \ L to$$ $$10.0 \ L. $$What is the work done by the system? ($$1 \ L\cdot atm = 101.3 \ J)$$

Accepted Answer

$$w = -1013 \ J$$

Question 8

Which of the following reactions is an example of a formation reaction for standard enthalpy of formation?

Accepted Answer

$$C(s) + O_2$(g) \rightarrow CO_2$(g)$$

Question 9

If the enthalpy change for a reaction is $$\Delta H = -250 \ kJ$$, which statement is true?

Accepted Answer

The reaction is exothermic and releases heat.

Question 10

Which formula is used to calculate the heat absorbed or released by a substance?

Accepted Answer

$$q = mC_s\Delta T$$

Question 11

A reaction has $$\Delta H = +120 \ kJ. $$What does this indicate about the reaction?

Accepted Answer

It is endothermic and absorbs heat.

Question 12

Which of the following best describes the process of calorimetry?

Accepted Answer

Measuring the amount of heat transferred during a chemical or physical process.

Question 13

Given the following reactions and their enthalpy changes:
$$A + B \rightarrow C \quad \Delta H = 122 \ J$$
$$2C \rightarrow 4A + 2B \quad \Delta H = ?$$
What is $$\Delta H$$ for the second reaction?

Accepted Answer

$$\Delta H = -244 \ J$$

Question 14

Which of the following is true about specific heat capacity?

Accepted Answer

It is the amount of heat required to raise the temperature of 1 gram of a substance by $$1^\circ C.$$

Question 15

If 100 g of water at $$80^\circ C is $$mixed with 100 g of water at $$20^\circ C$$, what will be the final temperature, assuming no heat loss?

Accepted Answer

$$T_f = 50^\circ C$$

Question 16

Which of the following is NOT a valid standard enthalpy of formation reaction?

Accepted Answer

$$2H_2(g) + O_2$(g) \rightarrow 2H_2O(l)$$

Question 17

Which statement about heat and work is correct?

Accepted Answer

Heat and work are path-dependent functions.

Question 18

If a reaction is reversed, what happens to the sign of $$\Delta H$$?

Accepted Answer

It becomes positive if it was negative, and vice versa.

Question 19

Which of the following best explains why the temperature of a substance increases when it absorbs heat?

Accepted Answer

The kinetic energy of its molecules increases.

Thermochemistry: First Law of Thermodynamics, Enthalpy, Hess’s Law, and Calorimetry

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