Q: A 32.5 g block of aluminum at 48.5°C is placed in 105.3 g of water at 15.4°C. Which equation would you use to find the final equilibrium temperature?

$$q_{\text{Al}} = -q$$_{\text{H}$$_2O}$$

Q: A reaction occurs in a bomb calorimeter and the temperature of the calorimeter increases by 3.41°C. If the heat capacity of the calorimeter is 4.90 kJ/°C, what is the heat of the reaction?

$$q_{\text{rxn}} = -4.90 \times 3.41 = -16.7 kJ$$

Q: Which of the following is the correct formula for calculating the standard enthalpy change of a reaction ($$\Delta H^\circ_{\text{rxn}}) $$using standard enthalpies of formation?

$$\Delta H^\circ_{\text{rxn}} = \sum n_p \Delta H_f^\circ(\text{products}) - \sum n_r \Delta H_f^\circ(\text{reactants})$$

Q: If the specific heat capacity ($$C_s) of $$water is 4.18 J/g·°C, how much heat is required to raise the temperature of 100.0 g of water from 25.0°C to 75.0°C?

$$q = 100.0 \times 4.18 \times (75.0 - 25.0) = 20,900 J$$

Question 1

Which of the following best describes the thermite reaction shown in the first image, where iron(III) oxide reacts with aluminum to produce iron and aluminum oxide?

Accepted Answer

It is an exothermic reaction because it releases heat to the surroundings.

Question 2

A student holds a hot cup of coffee, as shown in one of the images. Which statement best describes the direction of heat flow?

Accepted Answer

Heat flows from the coffee to the student's hands.

Question 3

Which equation correctly expresses the relationship between heat (q), heat capacity (C), and temperature change ($$ \Delta T $$)?

Accepted Answer

$$q = C 	imes \Delta T$$

Question 4

A 32.5 g block of aluminum at 48.5°C is placed in 105.3 g of water at 15.4°C. Which equation would you use to find the final equilibrium temperature?

Accepted Answer

$$q_{	ext{Al}} = -q$$_{	ext{H}$$_2O}$$

Question 5

Which of the following is a state function?

Accepted Answer

Internal energy (E)

Question 6

The first law of thermodynamics states:

Accepted Answer

Energy can be neither created nor destroyed, only transferred or transformed.

Question 7

Which of the following correctly expresses the change in internal energy ($$ \Delta E ) of a $$system?

Accepted Answer

$$\Delta E = q + w$$

Question 8

A reaction occurs in a bomb calorimeter and the temperature of the calorimeter increases by 3.41°C. If the heat capacity of the calorimeter is 4.90 kJ/°C, what is the heat of the reaction?

Accepted Answer

$$q_{	ext{rxn}} = -4.90 	imes 3.41 = -16.7 kJ$$

Question 9

Which of the following statements is true for an exothermic reaction?

Accepted Answer

$$\Delta H \u003c 0$$ and the reaction feels hot to the touch.

Question 10

Given the reaction: $$2 	ext{H}_2(g) + 	ext{O}_2(g) ightarrow 2 	ext{H}_2	ext{O}(g)$$, $$\Delta H_{	ext{rxn}} = -483.6 kJ. $$How much heat is released when 1 mole of $$	ext{H}_2$$ reacts?

Accepted Answer

241.8 kJ

Question 11

Which of the following is the correct formula for calculating the standard enthalpy change of a reaction ($$\Delta H^\circ_{	ext{rxn}}) $$using standard enthalpies of formation?

Accepted Answer

$$\Delta H^\circ_{	ext{rxn}} = \sum n_p \Delta H_f^\circ(	ext{products}) - \sum n_r \Delta H_f^\circ(	ext{reactants})$$

Question 12

A chemical equation is reversed. What happens to the sign of $$\Delta H_{	ext{rxn}}$$?

Accepted Answer

It changes sign.

Question 13

Which of the following best describes the energy transfer in a cold pack used for sports injuries?

Accepted Answer

The pack absorbs heat from the injury, making the reaction endothermic.

Question 14

If the specific heat capacity ($$C_s) of $$water is 4.18 J/g·°C, how much heat is required to raise the temperature of 100.0 g of water from 25.0°C to 75.0°C?

Accepted Answer

$$q = 100.0 	imes 4.18 	imes (75.0 - 25.0) = 20,900 J$$

Question 15

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

Accepted Answer

It is zero for pure elements in their standard state.

Question 16

A reaction is carried out in a coffee-cup calorimeter. If the temperature of the solution increases, what can you conclude about the reaction?

Accepted Answer

The reaction is exothermic.

Question 17

Which of the following is the correct sign convention for work (w) when work is done by the system on the surroundings?

Accepted Answer

w is negative

Question 18

If a chemical equation is multiplied by a factor of 2, what happens to $$\Delta H_{	ext{rxn}}$$?

Accepted Answer

$$\Delta H_{	ext{rxn}} is $$doubled.

Question 19

Which of the following best describes the relationship between the system and surroundings in the context of energy transfer?

Accepted Answer

Energy lost by the system is gained by the surroundings.

Chapter 7: Thermochemistry – Energy, Heat, and Enthalpy in Chemical Reactions

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