Q: A 2.00 kg object is moving at a speed of 3.00 m/s. What is its kinetic energy?

$$KE = \frac{1}{2}mv^2$ = \frac{1}{2} \times 2.00 \times (3.00)^2$ = 9.00\ J$$

Q: A 255 g sample of water is heated from 25.2°C to 90.5°C. How much heat (in kJ) is required? (Specific heat of water = 4.184 J/g·°C)

$$q = sm\Delta T = 4.184\ J/g\cdot ^\circ C \times 255\ g \times (90.5 - 25.2)^\circ C = 69,700\ J = 69.7\ kJ$$

Q: Which of the following is the correct expression for the standard enthalpy of reaction ($$\Delta H_{rxn}^\circ) $$using standard enthalpies of formation?

$$\Delta H_{rxn}^\circ = \sum n\Delta H_f^\circ (\text{products}) - \sum m\Delta H_f^\circ (\text{reactants})$$

Q: A bomb calorimeter has a heat capacity of 39.97 kJ/°C. If the temperature increases by 3.90°C during combustion of a 7.25 g cookie, what is the energy content per gram of the cookie?

$$q = C_{cal} \Delta T = 39.97\ kJ$$/^{\circ}$$C \times 3.90$$^{\circ}$$C = 155.9\ kJ$$;\ Energy\ per\ gram = \frac{155.9\ kJ}{7.25\ g} = 21.5\ kJ/g$

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 universe remains constant; energy may change forms but is neither created nor destroyed.

Question 2

A 2.00 kg object is moving at a speed of 3.00 m/s. What is its kinetic energy?

Accepted Answer

$$KE = \frac{1}{2}mv^2$ = \frac{1}{2} 	imes 2.00 	imes (3.00)^2$ = 9.00\ J$$

Question 3

Which of the following statements about exothermic and endothermic processes is correct?

Accepted Answer

Exothermic processes release heat to the surroundings, while endothermic processes absorb heat from the surroundings.

Question 4

A system absorbs 250 J of heat and does 75 J of work on its surroundings. What is the change in internal energy ($$\Delta U) of $$the system?

Accepted Answer

$$\Delta U = q + w = 250\ J + (-75\ J) = 175\ J$$

Question 5

Which of the following is a state function?

Accepted Answer

Internal energy ($$U)$$

Question 6

What is the specific heat capacity equation for calculating the heat required to raise the temperature of a substance?

Accepted Answer

$$q = sm\Delta T$$

Question 7

A 255 g sample of water is heated from 25.2°C to 90.5°C. How much heat (in kJ) is required? (Specific heat of water = 4.184 J/g·°C)

Accepted Answer

$$q = sm\Delta T = 4.184\ J/g\cdot ^\circ C 	imes 255\ g 	imes (90.5 - 25.2)^\circ C = 69,700\ J = 69.7\ kJ$$

Question 8

Which of the following best describes Hess's Law?

Accepted Answer

The enthalpy change for a reaction is the same whether it occurs in one step or multiple steps.

Question 9

Given the following reactions and their enthalpy changes:
$$\mathrm{C(graphite) + O_2$(g) \rightarrow CO_2$(g)}\ \Delta H = -393.5\ kJ$$
$$\mathrm{H_2$(g) + \frac{1}{2}O_2$(g) \rightarrow H_2O(l)}\ \Delta H = -285.8\ kJ$$
$$\mathrm{2C_2H_2(g) + 5O_2(g) \rightarrow 4CO_2(g) + 2H_2O(l)}\ \Delta H = -2598.8\ kJ$$
Calculate the standard enthalpy of formation of acetylene ($$\mathrm{C_2H_2}) in kJ/$$mol.

Accepted Answer

$$\Delta H_f = +226.6\ kJ/mol$$

Question 10

Which of the following is the correct expression for the standard enthalpy of reaction ($$\Delta H_{rxn}^\circ) $$using standard enthalpies of formation?

Accepted Answer

$$\Delta H_{rxn}^\circ = \sum n\Delta H_f^\circ (	ext{products}) - \sum m\Delta H_f^\circ (	ext{reactants})$$

Question 11

A bomb calorimeter has a heat capacity of 39.97 kJ/°C. If the temperature increases by 3.90°C during combustion of a 7.25 g cookie, what is the energy content per gram of the cookie?

Accepted Answer

$$q = C_{cal} \Delta T = 39.97\ kJ$$/^{\circ}$$C 	imes 3.90$$^{\circ}$$C = 155.9\ kJ$$;\ Energy\ per\ gram = \frac{155.9\ kJ}{7.25\ g} = 21.5\ kJ/g$

Question 12

Which of the following is true about the relationship between enthalpy ($$H$$), internal energy ($$U$$), pressure ($$P$$), and volume ($$V$$)?

Accepted Answer

$$H = U + PV$$

Question 13

If a chemical reaction is carried out at constant pressure and the system does 50 J of work while absorbing 200 J of heat, what is the change in enthalpy ($$\Delta H$$)?

Accepted Answer

$$\Delta H = q_p = 200\ J$$

Question 14

Which of the following statements about specific heat and heat capacity is correct?

Accepted Answer

Specific heat is the amount of heat required to raise the temperature of 1 g of a substance by 1°C.

Question 15

Which of the following is the correct sign convention for heat ($$q) $$and work ($$w) in $$thermodynamics?

Accepted Answer

Heat absorbed by the system: $$q \u003e 0$$; Work done by the system: $$w \u003c 0$$

Question 16

A chemical reaction at constant pressure has $$\Delta H = -890.4\ kJ. $$What does this value indicate?

Accepted Answer

The reaction is exothermic and releases 890.4 kJ of heat.

Question 17

Which of the following is the correct unit conversion for calories to joules?

Accepted Answer

$$1\ 	ext{cal} = 4.184\ 	ext{J}$$

Question 18

Which of the following best describes a closed system in thermodynamics?

Accepted Answer

A system that can exchange energy but not mass with its surroundings.

Physical Chemistry (CHEM 431) Syllabus and Course Information

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