Q: Calculate the heat ($$q) $$released when 100 g of water cools from 80°C to 30°C. (Specific heat of water $$= 4.184 \text{ J/g} \cdot ^\circ\text{C})$$

$$q = 100 \times 4.184 \times (80 - 30) = 20,920 \text{ J}$$

Q: A 50 g sample of metal at 100°C is placed in 100 g of water at 25°C. The final temperature is 30°C. If the specific heat of water is $$4.184 \text{ J/g} \cdot ^\circ\text{C}$$, what is the specific heat of the metal?

$$c = \frac{100 \times 4.184 \times (30-25)}{50 \times (100-30)} = 0.597 \text{ J/g} \cdot ^\circ\text{C}$$

Q: Which formula is used to calculate the heat absorbed or released by a substance?

$$q = m \times s \times \Delta T$$

Q: Which of the following reactions is endothermic?

$$\text{H}_2\text{O}(s) \rightarrow \text{H}_2\text{O}(l)$$ $$\Delta H = +6.01 \text{ kJ}$$

Q: A bomb calorimeter contains 2000 g of water and absorbs 4.2°C of temperature increase. If the heat capacity of the calorimeter is 453 J/°C, what is the total heat absorbed?

$$q = (2000 \times 4.184 \times 4.2) + (453 \times 4.2) = 35,944.8 \text{ J}$$

Q: Which equation is used to calculate the standard enthalpy of reaction ($$\Delta H^\circ_{rxn}) $$from standard enthalpies of formation?

$$\Delta H^\circ_{rxn} = \sum \Delta H^\circ_f (\text{products}) - \sum \Delta H^\circ_f (\text{reactants})$$

Question 1

Which of the following best describes the law of conservation of energy?

Accepted Answer

Energy can be transferred from one form to another, but the total quantity remains constant.

Question 2

Which type of energy is associated with the random motion of atoms and molecules?

Accepted Answer

Thermal energy

Question 3

A chemical reaction occurs in a flask, and the temperature of the surroundings increases. What type of process is this?

Accepted Answer

Exothermic

Question 4

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 5

If a gas expands against a constant external pressure, which formula is used to calculate the work done by the system?

Accepted Answer

$$w = -P \Delta V$$

Question 6

Which statement about enthalpy ($$\Delta H) is $$correct?

Accepted Answer

It is the heat flow into or out of a system at constant pressure.

Question 7

Given the thermochemical equation: $$2	ext{HgO}(s) ightarrow 2	ext{Hg}(l) + O_2$(g)$$, what happens to $$\Delta H if $$the reaction is reversed?

Accepted Answer

$$\Delta H$$ changes sign.

Question 8

Calculate the heat ($$q) $$released when 100 g of water cools from 80°C to 30°C. (Specific heat of water $$= 4.184 	ext{ J/g} \cdot ^\circ	ext{C})$$

Accepted Answer

$$q = 100 	imes 4.184 	imes (80 - 30) = 20,920 	ext{ J}$$

Question 9

Which of the following is true about the standard enthalpy of formation ($$\Delta H_f^\circ) of an $$element in its most stable form?

Accepted Answer

It is defined as zero.

Question 10

A 50 g sample of metal at 100°C is placed in 100 g of water at 25°C. The final temperature is 30°C. If the specific heat of water is $$4.184 	ext{ J/g} \cdot ^\circ	ext{C}$$, what is the specific heat of the metal?

Accepted Answer

$$c = \frac{100 	imes 4.184 	imes (30-25)}{50 	imes (100-30)} = 0.597 	ext{ J/g} \cdot ^\circ	ext{C}$$

Question 11

Which of the following is a state function?

Accepted Answer

Enthalpy

Question 12

The combustion of propane ($$	ext{C}_3	ext{H}_8) $$releases $$-2220 	ext{ kJ}$$ per mole. How much heat is released by burning $$44.1 	ext{ g} of $$propane? (Molar mass $$= 44.1 	ext{ g/mol})$$

Accepted Answer

$$-2220 	ext{ kJ}$$

Question 13

Which formula is used to calculate the heat absorbed or released by a substance?

Accepted Answer

$$q = m 	imes s 	imes \Delta T$$

Question 14

Which of the following reactions is endothermic?

Accepted Answer

$$	ext{H}_2	ext{O}(s) ightarrow 	ext{H}_2	ext{O}(l)$$ $$\Delta H = +6.01 	ext{ kJ}$$

Question 15

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

Accepted Answer

It allows exchange of energy but not mass with the surroundings.

Question 16

If the enthalpy of formation of $$	ext{CO}_2(g) is$$ $$-393.5 	ext{ kJ/mol}$$, what is the enthalpy change for the reaction: $$	ext{C(graphite)} + 	ext{O}_2(g) ightarrow 	ext{CO}_2(g)$$?

Accepted Answer

$$-393.5 	ext{ kJ}$$

Question 17

Which of the following is NOT a form of energy discussed in thermochemistry?

Accepted Answer

Magnetic energy

Question 18

A bomb calorimeter contains 2000 g of water and absorbs 4.2°C of temperature increase. If the heat capacity of the calorimeter is 453 J/°C, what is the total heat absorbed?

Accepted Answer

$$q = (2000 	imes 4.184 	imes 4.2) + (453 	imes 4.2) = 35,944.8 	ext{ J}$$

Question 19

Which equation is used to calculate the standard enthalpy of reaction ($$\Delta H^\circ_{rxn}) $$from standard enthalpies of formation?

Accepted Answer

$$\Delta H^\circ_{rxn} = \sum \Delta H^\circ_f (	ext{products}) - \sum \Delta H^\circ_f (	ext{reactants})$$

Thermochemistry and Conservation of Energy: Study Notes

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