Q: Which equation correctly relates heat flow ($$q$$), mass ($$m$$), specific heat ($$c$$), and temperature change ($$\Delta T) $$for a solution?

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

Q: If 1.00 g of gasoline (molar mass = 114.26 g/mol) is combusted and releases 48.1 kJ of energy per mole, how much heat is released?

$$0.421 \text{ mol} \times 48.1 \text{ kJ/mol} = 20.3 \text{ kJ}$$

Q: Which of the following reactions is a formation reaction?

$$\text{C} (s) + \frac{1}{2} \text{O}_2 (g) \rightarrow \text{CO} (g)$$

Question 1

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

Accepted Answer

A system that cannot exchange either energy or matter with its surroundings.

Question 2

Which equation correctly relates heat flow ($$q$$), mass ($$m$$), specific heat ($$c$$), and temperature change ($$\Delta T) $$for a solution?

Accepted Answer

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

Question 3

A student dissolves NaCl in water and observes the temperature of the solution decreases. Which term best describes this process?

Accepted Answer

Endothermic

Question 4

Which of the following is the correct expression for the change in internal energy ($$\Delta E) of a $$system?

Accepted Answer

$$\Delta E = q + w$$

Question 5

If 1.00 g of gasoline (molar mass = 114.26 g/mol) is combusted and releases 48.1 kJ of energy per mole, how much heat is released?

Accepted Answer

$$0.421 	ext{ mol} 	imes 48.1 	ext{ kJ/mol} = 20.3 	ext{ kJ}$$

Question 6

Which of the following reactions is a formation reaction?

Accepted Answer

$$	ext{C} (s) + \frac{1}{2} 	ext{O}_2 (g) ightarrow 	ext{CO} (g)$$

Question 7

Which statement about bond energies is correct?

Accepted Answer

Breaking bonds requires energy, while forming bonds releases energy.

Question 8

Given the reaction: $$	ext{Mg} (s) + 2	ext{HCl} (aq) ightarrow 	ext{H}_2 (g) + 	ext{MgCl}_2 (aq)$$, if 30.0 g of Mg reacts at 1.00 atm and 25°C, what is the work done by the system (in kJ)? (Assume $$w = -P\Delta V$$ and $$1$$ mol $$	ext{Mg}$$ produces $$1$$ mol $$	ext{H}_2$$ gas.)

Accepted Answer

$$-2.24 kJ$$

Question 9

Which of the following is true about enthalpy ($$\Delta H) $$and heat ($$q) at $$constant pressure?

Accepted Answer

$$\Delta H$$ equals $$q at $$constant pressure.

Question 10

A calorimeter contains 100.0 g of water at 25°C. If 2.00 g of NaOH is dissolved and the temperature rises to 28°C, what is the heat absorbed by the solution? ($$c_{	ext{H}_2$$	ext{O}} = 4.184$$ J/g°C)

Accepted Answer

$$836.8 J$$

Question 11

Which of the following best describes Hess's Law?

Accepted Answer

The enthalpy change of a reaction is independent of the pathway and depends only on the initial and final states.

Question 12

Using bond energies, estimate the enthalpy change ($$\Delta H) $$for the reaction: $$	ext{H}_2 (g) + 	ext{Cl}_2 (g) ightarrow 2	ext{HCl} (g). $$Given: $$D(	ext{H}-	ext{H}) = 432 kJ/$$mol, $$D(	ext{Cl}-	ext{Cl}) = 242 kJ/$$mol, $$D(	ext{H}-	ext{Cl}) = 431 kJ/$$mol.

Accepted Answer

$$-184 kJ$$

Question 13

Which of the following statements about exothermic reactions is correct?

Accepted Answer

Exothermic reactions release heat to the surroundings.

Question 14

If the enthalpy of combustion of hydrazine ($$	ext{N}_2	ext{H}_4) is$$ $$-316 kJ/$$mol, how many grams are needed to produce $$351 kJ of $$heat?

Accepted Answer

$$14.6 g$$

Question 15

Which of the following is a correct application of the first law of thermodynamics?

Accepted Answer

The total energy of an isolated system remains constant.

Question 16

Which of the following would increase the work done ON the surroundings during a chemical reaction at constant pressure?

Accepted Answer

An increase in the volume of the system ($$\Delta V \u003e 0)$$

Question 17

Which of the following is the correct formula for calculating work done by a gas at constant pressure?

Accepted Answer

$$w = -P\Delta V$$

Question 18

A reaction is carried out in a coffee cup calorimeter. Which of the following is assumed to be true?

Accepted Answer

The pressure is constant and the heat measured equals $$\Delta H.$$

Question 19

Which of the following processes would release more $$	ext{CO}_2 to $$the atmosphere: combustion of gasoline or ethanol (assuming equal energy released)?

Accepted Answer

Combustion of gasoline releases more $$	ext{CO}_2.$$

Thermochemistry and Enthalpy: Study Notes for General Chemistry

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