Q: A 2.0 kg object is moving at a speed of 3.0 m/s. What is its kinetic energy?

$$E_k = \frac{1}{2}mv^2$ = \frac{1}{2} \times 2.0 \times (3.0)^2$ = 9.0\ \mathrm{J}$$

Q: A 350 g can of soda (specific heat $$= 4.18\ \mathrm{J/g\cdot ^\circ C}) is $$cooled from $$25^\circ \mathrm{C} to$$ $$3^\circ \mathrm{C}. $$How much heat is released?

$$q = (4.18\ \mathrm{J/g\cdot ^\circ C}) \times 350\ \mathrm{g} \times (3 - 25)\ ^\circ \mathrm{C} = -32,102\ \mathrm{J}$$

Q: Given the following standard enthalpies of formation: $$\Delta H_f^\circ (\mathrm{CO_2$(g)}) = -393.5\ \mathrm{kJ/mol}$$, $$\Delta H_f^\circ (\mathrm{H_2O(l)}) = -285.8\ \mathrm{kJ/mol}$$, $$\Delta H_f^\circ (\mathrm{C_6H_{12}O_6$(s)}) = -1260\ \mathrm{kJ/mol}$$, calculate the standard enthalpy change for the reaction: $$6\mathrm{CO_2$(g)} + 6\mathrm{H_2O(l)} \rightarrow \mathrm{C_6H_{12}O_6$(s)} + 6\mathrm{O_2$(g)}.$$

$$\Delta H^\circ = [-1260 + 0] - [6 \times (-393.5) + 6 \times (-285.8)] = 2802\ \mathrm{kJ}$$

Question 1

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

Accepted Answer

Energy can be converted from one form to another, but cannot be created or destroyed.

Question 2

A 2.0 kg object is moving at a speed of 3.0 m/s. What is its kinetic energy?

Accepted Answer

$$E_k = \frac{1}{2}mv^2$ = \frac{1}{2} 	imes 2.0 	imes (3.0)^2$ = 9.0\ \mathrm{J}$$

Question 3

Which of the following is an example of potential energy being converted to kinetic energy in a real-world scenario?

Accepted Answer

A compressed spring being released and launching a ball.

Question 4

Which equation correctly represents the calculation of work done by a gas during expansion at constant pressure?

Accepted Answer

$$w = -P \Delta V$$

Question 5

A chemical reaction in a flask releases 500 J of heat to the surroundings and does 200 J of work on the surroundings. What is the change in internal energy ($$\Delta E) of $$the system?

Accepted Answer

$$\Delta E = q + w = -500\ \mathrm{J} + (-200\ \mathrm{J}) = -700\ \mathrm{J}$$

Question 6

Which of the following is a state function?

Accepted Answer

Enthalpy ($$H)$$

Question 7

For the reaction $$\mathrm{CH_4$(g) + 2O_2(g) \rightarrow CO_2$(g) + 2H_2O(g)}$$, $$\Delta H = -802\ \mathrm{kJ}. $$What does the negative sign indicate?

Accepted Answer

The reaction is exothermic and releases heat to the surroundings.

Question 8

Which of the following best describes the difference between specific heat and molar heat capacity?

Accepted Answer

Specific heat is the heat required to raise the temperature of 1 gram of a substance by 1°C, while molar heat capacity is the heat required to raise the temperature of 1 mole of a substance by 1°C.

Question 9

A 350 g can of soda (specific heat $$= 4.18\ \mathrm{J/g\cdot ^\circ C}) is $$cooled from $$25^\circ \mathrm{C} to$$ $$3^\circ \mathrm{C}. $$How much heat is released?

Accepted Answer

$$q = (4.18\ \mathrm{J/g\cdot ^\circ C}) 	imes 350\ \mathrm{g} 	imes (3 - 25)\ ^\circ \mathrm{C} = -32,102\ \mathrm{J}$$

Question 10

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

Accepted Answer

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

Question 11

Which of the following best describes Hess's Law?

Accepted Answer

The enthalpy change for a reaction is the same, regardless of the number of steps or pathway taken.

Question 12

Given the following standard enthalpies of formation: $$\Delta H_f^\circ (\mathrm{CO_2$(g)}) = -393.5\ \mathrm{kJ/mol}$$, $$\Delta H_f^\circ (\mathrm{H_2O(l)}) = -285.8\ \mathrm{kJ/mol}$$, $$\Delta H_f^\circ (\mathrm{C_6H_{12}O_6$(s)}) = -1260\ \mathrm{kJ/mol}$$, calculate the standard enthalpy change for the reaction: $$6\mathrm{CO_2$(g)} + 6\mathrm{H_2O(l)} \rightarrow \mathrm{C_6H_{12}O_6$(s)} + 6\mathrm{O_2$(g)}.$$

Accepted Answer

$$\Delta H^\circ = [-1260 + 0] - [6 	imes (-393.5) + 6 	imes (-285.8)] = 2802\ \mathrm{kJ}$$

Question 13

Which of the following processes is favored by both a decrease in enthalpy ($$\Delta H  0$$)?

Accepted Answer

A spontaneous process

Question 14

Which equation correctly relates Gibbs free energy change ($$\Delta G$$), enthalpy change ($$\Delta H$$), and entropy change ($$\Delta S) at $$temperature $$T$$?

Accepted Answer

$$\Delta G = \Delta H - T\Delta S$$

Question 15

Which of the following best describes a spontaneous process?

Accepted Answer

A process that, once started, proceeds on its own without continuous external influence.

Question 16

Which of the following statements about entropy ($$S) is $$correct?

Accepted Answer

Entropy is a measure of molecular randomness or disorder in a system.

Question 17

Which of the following reactions would you expect to have a positive entropy change ($$\Delta S \u003e 0$$)?

Accepted Answer

$$\mathrm{NH_4Cl(s) \rightarrow NH_3$(g) + HCl(g)}$$

Chapter 9: Thermochemistry – Chemical Energy and Its Conservation

Guida di studio - Domande di pratica

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