Q: A 15.0 g piece of nickel at 100.0°C is dropped into 55.0 g of water at 23.0°C. If the final equilibrium temperature is 27.1°C, what is the heat lost by the nickel? (Given: $$C_{nickel} = 0.444 \ J/g \cdot K)$$

$$q = 15.0 \times 0.444 \times (27.1 - 100.0) = -486.6 \ J$$

Q: Calculate the amount of heat required to raise the temperature of 1.01 kg of water from 0.05°C to 35.81°C. (Specific heat of water $$= 4.184 \ J/g \cdot K)$$

$$q = 1010 \times 4.184 \times (35.81 - 0.05) = 148,927 \ J$$

Q: A 13.8 g piece of zinc is heated to 98.8°C and dropped into 45.0 g of water at 25.0°C. The final temperature is 27.1°C. What is the specific heat capacity of zinc? (Specific heat of water $$= 4.184 \ J/g \cdot K)$$

$$C_{Zn} = \frac{45.0 \times 4.184 \times (27.1 - 25.0)}{13.8 \times (98.8 - 27.1)} = 0.389 \ J/g \cdot K$$

Q: Which equation would you use to calculate the heat required to change the temperature of a substance?

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

Question 1

Which of the following best describes an isolated system in thermochemistry?

Accepted Answer

A system that exchanges neither energy nor matter with its surroundings.

Question 2

A metal spoon and a wooden spoon are both left at room temperature. Why does the metal spoon feel colder to the touch?

Accepted Answer

Because metal conducts heat away from your hand more efficiently than wood.

Question 3

Which equation represents the First Law of Thermodynamics?

Accepted Answer

$$\Delta E = q + w$$

Question 4

A 15.0 g piece of nickel at 100.0°C is dropped into 55.0 g of water at 23.0°C. If the final equilibrium temperature is 27.1°C, what is the heat lost by the nickel? (Given: $$C_{nickel} = 0.444 \ J/g \cdot K)$$

Accepted Answer

$$q = 15.0 	imes 0.444 	imes (27.1 - 100.0) = -486.6 \ J$$

Question 5

Which of the following statements about enthalpy ($$\Delta H) is $$correct?

Accepted Answer

Enthalpy change is a state function and depends only on the initial and final states.

Question 6

Calculate the amount of heat required to raise the temperature of 1.01 kg of water from 0.05°C to 35.81°C. (Specific heat of water $$= 4.184 \ J/g \cdot K)$$

Accepted Answer

$$q = 1010 	imes 4.184 	imes (35.81 - 0.05) = 148,927 \ J$$

Question 7

Which of the following is an example of an exothermic process?

Accepted Answer

Combustion of gasoline in a car engine.

Question 8

What is the specific heat capacity of mercury in J/g·K if its molar heat capacity is 28.1 J/mol·K? (Atomic mass of Hg = 200.59 g/mol)

Accepted Answer

$$C = \frac{28.1}{200.59} = 0.140 \ J/g \cdot K$$

Question 9

Which of the following best explains why heat flows from hot to cold objects?

Accepted Answer

Heat flows from hot to cold due to a temperature gradient until thermal equilibrium is reached.

Question 10

A 13.8 g piece of zinc is heated to 98.8°C and dropped into 45.0 g of water at 25.0°C. The final temperature is 27.1°C. What is the specific heat capacity of zinc? (Specific heat of water $$= 4.184 \ J/g \cdot K)$$

Accepted Answer

$$C_{Zn} = \frac{45.0 	imes 4.184 	imes (27.1 - 25.0)}{13.8 	imes (98.8 - 27.1)} = 0.389 \ J/g \cdot K$$

Question 11

Which of the following is NOT a state function?

Accepted Answer

Work ($$w)$$

Question 12

Which equation would you use to calculate the heat required to change the temperature of a substance?

Accepted Answer

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

Question 13

Which of the following statements about Hess's Law is correct?

Accepted Answer

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

Question 14

Which process is endothermic?

Accepted Answer

Melting of ice.

Question 15

A coffee-cup calorimeter contains 125.0 g of water at 24.0°C. 11.0 g of CaCl2(s) is added. The heat of dissolution is -81 kJ/mol. What happens to the temperature of the solution?

Accepted Answer

The temperature increases because the process is exothermic.

Question 16

Which of the following is true for an exothermic reaction?

Accepted Answer

The system releases heat to the surroundings.

Question 17

Which of the following is the correct thermochemical equation for the formation of 1 mole of water vapor from its elements?

Accepted Answer

$$H_2(g$$) + \frac{1}{2}$$O_2(g$$) \rightarrow H_2O(g)$$

Question 18

Which of the following is a correct sign convention for heat and work in thermochemistry?

Accepted Answer

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

Question 19

Which of the following is true about the heat of reaction?

Accepted Answer

It is the energy flow to or from the surroundings due to a reaction taking place.

Thermochemistry: Energy and Chemical Reactions

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