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

$$\Delta H^\circ_{rxn} = \Sigma n \Delta H_f^\circ (\text{products}) - \Sigma n \Delta H_f^\circ (\text{reactants})$$

Question 1

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

Accepted Answer

The total energy of the universe is constant.

Question 2

A chemical reaction in a beaker causes the temperature of the surroundings to increase. Which statement is correct?

Accepted Answer

The reaction is exothermic and releases heat to the surroundings.

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 student burns a piece of wood in a calorimeter. Which of the following best describes the system and surroundings in this experiment?

Accepted Answer

The system is the burning wood; the surroundings are everything else, including the calorimeter.

Question 5

Which of the following processes is endothermic?

Accepted Answer

Sweat evaporating from the skin.

Question 6

Calculate the kinetic energy of a 2 kg object moving at 3 m/s. Use $$KE = \frac{1}{2}mv^2$.

Accepted Answer

$$9 J$$

Question 7

Which of the following is true about state functions?

Accepted Answer

Their values depend only on the initial and final states, not the path taken.

Question 8

Given the following reactions and their enthalpy changes:

$$A + 2B \rightarrow C,\ \Delta H_1$

C$$ \rightarrow 2D,\ \Delta $$H_2$$

What is the enthalpy change for $$A + 2B \rightarrow 2D$$?

Accepted Answer

$$\Delta H_1$ + \Delta H_2$

Question 9

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

Accepted Answer

It is the enthalpy change for forming 1 mole of a compound from its elements in their standard states.

Question 10

A reaction has $$\Delta H = -250 kJ. $$Which of the following is true?

Accepted Answer

The reaction is exothermic and releases 250 kJ of heat.

Question 11

Which of the following best describes the energy change when an ice cube melts?

Accepted Answer

It is an endothermic process; heat is absorbed from the surroundings.

Question 12

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

Accepted Answer

$$\Delta H^\circ_{rxn} = \Sigma n \Delta H_f^\circ (	ext{products}) - \Sigma n \Delta H_f^\circ (	ext{reactants})$$

Question 13

Which of the following is NOT a form of kinetic energy?

Accepted Answer

Chemical energy

Question 14

A coffee-cup calorimeter is used to measure the heat of a reaction at constant pressure. Which thermodynamic quantity does it directly measure?

Accepted Answer

Enthalpy change ($$\Delta H)$$

Question 15

Which of the following statements about lattice energy is correct?

Accepted Answer

Lattice energy increases as the charge of the ions increases.

Question 16

A reaction occurs in a closed container at constant pressure and does work on the surroundings by expanding against a constant external pressure. Which equation correctly describes the relationship between $$\Delta H$$, $$\Delta E$$, and $$P\Delta V$$?

Accepted Answer

$$\Delta H = \Delta E + P\Delta V$$

Question 17

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

Accepted Answer

Enthalpy change ($$\Delta H)$$

Question 18

A 100 g sample of water is heated from 25°C to 35°C. How many calories of energy are required? ($$1\ 	ext{cal} = $$ energy to raise 1 g water by 1°C)

Accepted Answer

1000 cal

Question 19

Which of the following best describes the standard state of a substance?

Accepted Answer

A pure gas at 1 atm, a pure solid or liquid at 1 atm and 25°C, or a solution at 1 M concentration.

CHEM 131 Chapter 7: Thermochemistry and Thermodynamics: Study Notes for General Chemistry

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