Q: Which of the following is the correct formula to calculate the heat required to raise the temperature of 50 g of water from 20°C to 80°C? (Specific heat of water = $$4.184 J/g$$°C)

$$q = 50 \times 4.184 \times (80 - 20)$$

Q: A 25.0 g sample of copper ($$s = 0.384 J/g$$°C) is heated from $$20.0$$°C to $$50.0$$°C. How much heat is absorbed?

$$q = 25.0 \times 0.384 \times (50.0 - 20.0) = 288 J$$

Q: A calorimeter contains 100 g of water at $$25.0$$°C. If 2.00 kJ of heat is added, what is the final temperature? (Specific heat of water = $$4.184 J/g$$°C)

$$T_{final} = 25.0 + \frac{2000}{100 \times 4.184} = 29.8$$°C

Q: Which of the following is the correct expression for calculating the standard enthalpy change of a reaction using standard enthalpies of formation?

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

Question 1

Which of the following statements best describes the Law of Conservation of Energy?

Accepted Answer

Energy is neither created nor destroyed, but can be converted from one form to another.

Question 2

A chemical reaction in a vessel releases 250 kJ of heat to the surroundings. Which term best describes this process?

Accepted Answer

Exothermic reaction

Question 3

How much energy in joules is equivalent to 3.5 kilocalories (kcal)?

Accepted Answer

$$3.5 	imes 4184 = 14644 J$$

Question 4

Which of the following is the correct formula to calculate the heat required to raise the temperature of 50 g of water from 20°C to 80°C? (Specific heat of water = $$4.184 J/g$$°C)

Accepted Answer

$$q = 50 	imes 4.184 	imes (80 - 20)$$

Question 5

A reaction has $$\Delta H = -890 kJ. $$What does this value indicate about the reaction?

Accepted Answer

The reaction releases 890 kJ of heat to the surroundings.

Question 6

If the equation $$N_2(g) + 3H_2(g$$) \rightarrow 2NH_3(g)$$ has $$\Delta H = -92$$ kJ, what is $$\Delta H$$ for the reverse reaction?

Accepted Answer

$$+92 kJ$$

Question 7

Calculate the heat evolved when 10.0 g of $$CH_4$$ burns completely in oxygen. ($$\Delta H = -890 kJ/$$mol, molar mass $$CH_4 = 16.05$ g/mol)

Accepted Answer

$$-554 kJ$$

Question 8

Which equation would you use to calculate the heat absorbed by a calorimeter with a heat capacity of $$15.0 kJ$$/°C when the temperature increases from $$22.0$$°C to $$27.0$$°C?

Accepted Answer

$$q = C \Delta T$$

Question 9

A 25.0 g sample of copper ($$s = 0.384 J/g$$°C) is heated from $$20.0$$°C to $$50.0$$°C. How much heat is absorbed?

Accepted Answer

$$q = 25.0 	imes 0.384 	imes (50.0 - 20.0) = 288 J$$

Question 10

Which of the following best describes the difference between a system and its surroundings in thermochemistry?

Accepted Answer

The system is the part of the universe being studied, while the surroundings are everything else.

Question 11

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

Accepted Answer

It is zero for all elements in their most stable form at 1 atm and 25°C.

Question 12

Given the reaction $$CH_4(g) + 2O_2(g$$) \rightarrow $$CO_2(g) + 2H_2O(g$$)$$ and $$\Delta H = -890$$ kJ, how much heat is released when 32.0 g of O_2$ reacts completely?

Accepted Answer

$$-445 kJ$$

Question 13

Which of the following is a correct application of Hess's Law?

Accepted Answer

The enthalpy change for a reaction is the sum of the enthalpy changes for a series of reactions that add up to the overall reaction.

Question 14

A calorimeter contains 100 g of water at $$25.0$$°C. If 2.00 kJ of heat is added, what is the final temperature? (Specific heat of water = $$4.184 J/g$$°C)

Accepted Answer

$$T_{final} = 25.0 + \frac{2000}{100 	imes 4.184} = 29.8$$°C

Question 15

Which of the following reactions is endothermic?

Accepted Answer

$$NH_4NO_3(s) \rightarrow NH_4$^+(aq) + NO_3$^-(aq)$$ with $$q = +36 kJ$$

Question 16

Which of the following is the correct expression for calculating the standard enthalpy change of a reaction using standard enthalpies of formation?

Accepted Answer

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

Question 17

A student mixes 50.0 mL of 1.0 M HCl with 50.0 mL of 1.0 M NaOH in a coffee-cup calorimeter. The temperature rises from $$22.0$$°C to $$28.0$$°C. Assuming the solution has the same density and specific heat as water ($$4.184 J/g$$°C), what is the heat released?

Accepted Answer

$$q = 100.0 	imes 4.184 	imes (28.0 - 22.0) = 2510 J$$

Question 18

Which of the following is NOT a correct unit for energy?

Accepted Answer

gram (g)

Thermochemistry: Study Notes (General Chemistry, Unit 5)

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