Q: A system absorbs 150 J of heat and does 50 J of work on the surroundings. What is the change in internal energy ($$\Delta U) of $$the system?

$$\Delta U = 150\ \text{J} - 50\ \text{J} = 100\ \text{J}$$

Q: How much heat is required to raise the temperature of 100 g of water from 25°C to 75°C? ($$c = 4.18\ \text{J/g}^\circ\text{C})$$

$$q = 100 \times 4.18 \times (75-25) = 20,900\ \text{J}$$

Q: A bomb calorimeter contains 1.00 g of glucose ($$C_6H_{12}O_6$) and measures a temperature increase of 2.50°C. If the heat capacity of the calorimeter is 10.0 kJ/°C, what is the energy released by the combustion?

$$q = 10.0 \times 2.50 = 25.0\ \text{kJ}$$

Q: Given the reaction: $$2H_2 + O_2$ \rightarrow 2H_2O$$, and $$\Delta H = -572 kJ$$, how much heat is released when 4.0 g of $$H_2$$ reacts?

Heat released = $$-572 \times \frac{4.0/2.02}{2} = -566 kJ$

Q: In a coffee-cup calorimeter, 50.0 mL of 1.0 M HCl is mixed with 50.0 mL of 1.0 M NaOH. The temperature rises by 6.0°C. If the solution has a density of 1.0 g/mL and a specific heat of 4.18 J/g°C, what is the heat evolved?

$$q = 100 \times 4.18 \times 6.0 = 2,508\ \text{J}$$

Question 1

Which of the following statements best describes the difference between an ideal gas and a real gas?

Accepted Answer

Real gases deviate from the ideal gas law at high pressures and low temperatures due to intermolecular forces and molecular volume.

Question 2

Which of the following is NOT a form of energy?

Accepted Answer

Entropy

Question 3

Convert 250 calories to joules. (1 cal = 4.184 J)

Accepted Answer

$$250 	imes 4.184 = 1046 J$$

Question 4

A system absorbs 150 J of heat and does 50 J of work on the surroundings. What is the change in internal energy ($$\Delta U) of $$the system?

Accepted Answer

$$\Delta U = 150\ 	ext{J} - 50\ 	ext{J} = 100\ 	ext{J}$$

Question 5

How much heat is required to raise the temperature of 100 g of water from 25°C to 75°C? ($$c = 4.18\ 	ext{J/g}^\circ	ext{C})$$

Accepted Answer

$$q = 100 	imes 4.18 	imes (75-25) = 20,900\ 	ext{J}$$

Question 6

Which of the following best describes pressure-volume work?

Accepted Answer

Work done by a system at constant pressure is given by $$w = -P\Delta V.$$

Question 7

A bomb calorimeter contains 1.00 g of glucose ($$C_6H_{12}O_6$) and measures a temperature increase of 2.50°C. If the heat capacity of the calorimeter is 10.0 kJ/°C, what is the energy released by the combustion?

Accepted Answer

$$q = 10.0 	imes 2.50 = 25.0\ 	ext{kJ}$$

Question 8

Which of the following processes is endothermic?

Accepted Answer

Melting of ice at 0°C

Question 9

Given the reaction: $$2H_2 + O_2$ \rightarrow 2H_2O$$, and $$\Delta H = -572 kJ$$, how much heat is released when 4.0 g of $$H_2$$ reacts?

Accepted Answer

Heat released = $$-572 	imes \frac{4.0/2.02}{2} = -566 kJ$

Question 10

In a coffee-cup calorimeter, 50.0 mL of 1.0 M HCl is mixed with 50.0 mL of 1.0 M NaOH. The temperature rises by 6.0°C. If the solution has a density of 1.0 g/mL and a specific heat of 4.18 J/g°C, what is the heat evolved?

Accepted Answer

$$q = 100 	imes 4.18 	imes 6.0 = 2,508\ 	ext{J}$$

Question 11

If the enthalpy of a reaction doubles when the coefficients of the reaction are doubled, what does this indicate about enthalpy?

Accepted Answer

Enthalpy is an extensive property.

Question 12

Which of the following equations correctly calculates the standard enthalpy change for the reaction: $$C_2H_4(g) + H_2$(g) \rightarrow C_2H_6(g)$$, given the standard enthalpies of formation?

Accepted Answer

$$\Delta H^\circ_{rxn} = \Delta H^\circ_f[C_2H_6(g)] - (\Delta H^\circ_f[C_2H_4(g)] + \Delta H^\circ_f[H_2$(g)])$$

Question 13

A sample of gas behaves non-ideally at high pressure because:

Accepted Answer

Intermolecular forces become significant.

Question 14

Which of the following is a correct conversion between energy units?

Accepted Answer

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

Question 15

A reaction in a bomb calorimeter releases 5000 J of heat. What is the sign of $$\Delta E$$ for the system?

Accepted Answer

$$\Delta E is $$negative

Question 16

Which of the following scenarios best illustrates the first law of thermodynamics?

Accepted Answer

A battery loses energy as heat and work, but the total energy change equals the sum of heat and work.

Question 17

If a chemical reaction in a coffee-cup calorimeter absorbs heat from the solution, what type of process is this?

Accepted Answer

Endothermic

Question 18

Which of the following would increase the enthalpy change of a reaction?

Accepted Answer

Doubling the amount of reactants

Question 19

Calculate the standard enthalpy change for the reaction: $$N_2(g) + 3H_2(g$$) \rightarrow 2NH_3(g)$$, given $$\Delta H^\circ_f[$$NH_3(g$$)] = -46.0$$ kJ/mol, $$\Delta H^\circ_f[$$N_2(g$$)] = 0$$, $$\Delta H^\circ_f[$$H_2(g$$)] = 0$$.

Accepted Answer

$$\Delta H^\circ_{rxn} = 2 	imes (-46.0) - [0 + 3 	imes 0] = -92.0 kJ$$

Study Guide: Thermochemistry and Real Gases (Chapters 6.10 & 7)

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