Q: A ball with a mass of 2 kg is dropped from a height of 5 meters. What is its potential energy just before it is dropped? (Use $$g = 9.8 \text{ m/s}^2)$$

$$PE = mgh = 2 \times 9.8 \times 5 = 98 \text{ J}$$

Q: A system releases 150 J of energy as heat to its surroundings and does 50 J of work on the surroundings. What is the change in internal energy of the system?

$$\Delta E = q + w = -150 \text{ J} + (-50 \text{ J}) = -200 \text{ J}$$

Question 1

Which of the following best describes the law of conservation of energy as it applies to chemical reactions?

Accepted Answer

The total energy of the system and surroundings remains constant; energy is neither created nor destroyed.

Question 2

A ball with a mass of 2 kg is dropped from a height of 5 meters. What is its potential energy just before it is dropped? (Use $$g = 9.8 	ext{ m/s}^2)$$

Accepted Answer

$$PE = mgh = 2 	imes 9.8 	imes 5 = 98 	ext{ J}$$

Question 3

Which of the following is an example of kinetic energy?

Accepted Answer

A moving car traveling down the highway.

Question 4

Thermal energy is best described as:

Accepted Answer

A type of kinetic energy arising from the motion of atoms or molecules.

Question 5

A system releases 150 J of energy as heat to its surroundings and does 50 J of work on the surroundings. What is the change in internal energy of the system?

Accepted Answer

$$\Delta E = q + w = -150 	ext{ J} + (-50 	ext{ J}) = -200 	ext{ J}$$

Question 6

Which of the following statements about state functions is correct?

Accepted Answer

Internal energy is a state function because it depends only on the initial and final states.

Question 7

In the reaction $$\mathrm{C(s) + O_2$(g) \rightarrow CO_2$(g)}$$, what happens to the internal energy of the system?

Accepted Answer

The internal energy of the system decreases and energy is released to the surroundings.

Question 8

Which equation correctly relates the change in internal energy to heat and work?

Accepted Answer

$$\Delta E = q + w$$

Question 9

A cup of hot coffee cools down when left in a room. Which statement best describes the energy flow?

Accepted Answer

Energy flows from the coffee into the surroundings.

Question 10

Which of the following is NOT a unit of energy?

Accepted Answer

Newton (N)

Question 11

A white ball with 5.0 J of kinetic energy collides with a purple ball and loses 2.0 J as heat. What is the change in energy of the white ball?

Accepted Answer

$$\Delta E = -5.0 	ext{ J}$$

Question 12

Which of the following best describes potential energy?

Accepted Answer

Energy associated with the position or composition of an object.

Question 13

If energy flows into a system from the surroundings, what is the sign of $$\Delta E_{system}$$?

Accepted Answer

$$\Delta E_{system} \u003e 0$$

Question 14

Which process is an example of work being done by a system?

Accepted Answer

A gas expanding against a piston.

Question 15

A chemical reaction occurs in a closed container. The reactants have a higher internal energy than the products. What is true about the energy flow?

Accepted Answer

Energy flows out of the system into the surroundings.

Question 16

Which of the following is a correct statement about heat and work?

Accepted Answer

Heat and work are ways energy can be exchanged between system and surroundings.

Question 17

A moving car uses gasoline to power its engine. What type of energy transformation occurs?

Accepted Answer

Chemical potential energy is converted to kinetic and thermal energy.

Question 18

Which of the following best describes a system in thermochemistry?

Accepted Answer

The part of the universe under study, usually where the chemical reaction occurs.

Question 19

If a reaction absorbs energy from the surroundings, what is the sign of $$\Delta E_{reaction}$$?

Accepted Answer

$$\Delta E_{reaction} \u003e 0$$

Question 20

Which of the following is true about the sum of the energy changes in the system and surroundings according to the first law of thermodynamics?

Accepted Answer

$$\Delta E_{system} + \Delta E_{surroundings} = 0$$

7.2-7.3 Thermochemistry: The Nature and Flow of Energy

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