Q: A 0.50 kg ball is dropped from a height of 10.0 m. Ignoring air resistance, what is the velocity of the ball just before it hits the ground? (Use $$g = 9.8 \ \mathrm{m/s^2$})$$

$$v = \sqrt{2gh} = \sqrt{2 \times 9.8 \times 10.0} = 14.0 \ \mathrm{m/s}$$

Q: A 120.0 g sample of water is cooled from $$90^\circ \mathrm{C} to$$ $$45^\circ \mathrm{C}. If $$the specific heat capacity of water is $$4.184 \ \mathrm{J/g \cdot ^\circ C}$$, how much heat is released?

$$q = m c \Delta T = 120.0 \times 4.184 \times (45 - 90) = -22,396.8 \ \mathrm{J}$$

Q: A refrigerator uses $$780 \ \mathrm{kWh} of $$electrical energy per year. How many kilocalories does it use in three years? ($$1 \ \mathrm{kWh} = 860 \ \mathrm{kcal})$$

$$780 \times 3 \times 860 = 2,010,600 \ \mathrm{kcal}$$

Q: A 15.7 g sample of silver raises its temperature by $$17.2^\circ \mathrm{C}$$ when it absorbs $$684.5 \ \mathrm{J} of $$heat. What is its molar heat capacity? (Molar mass of Ag = $$107.87 \ \mathrm{g/mol})$$

$$C_{\text{molar}} = \frac{q}{n \Delta T} = \frac{684.5}{(15.7/107.87) \times 17.2} = 28.0 \ \mathrm{J/mol \cdot ^\circ C}$$

Q: A gas expands from $$4.3 \ \mathrm{L} to$$ $$8.2 \ \mathrm{L} at a $$constant pressure of $$931 \ \mathrm{mmHg}. If $$the system absorbs $$2.34 \ \mathrm{kJ} of $$energy as heat, what is the change in internal energy? ($$1 \ \mathrm{L \cdot atm} = 101.3 \ \mathrm{J}$$, $$1 \ \mathrm{atm} = 760 \ \mathrm{mmHg})$$

$$\Delta E = q + w = 2,340 \ \mathrm{J} + [-(931/760) \times (8.2-4.3) \times 101.3] = 2,340 - 509 = 1,831 \ \mathrm{J}$$

Q: A 50.0 g sample of heated metal is placed into 822.5 g of water at $$32.08^\circ \mathrm{C}. If $$the metal gains $$14.55 \ \mathrm{kJ} of $$energy, what was the initial temperature of the water? (Specific heat of water $$= 4.184 \ \mathrm{J/g \cdot ^\circ C})$$

$$q = m c \Delta T \rightarrow 14,550 = 822.5 \times 4.184 \times (32.08 - T_i) \rightarrow T_i = 28.6^\circ \mathrm{C}$$

Q: A chemist wishes to determine the final temperature of $$30.0 \ \mathrm{g} of a $$metal ore placed into an insulated beaker containing $$615.5 \ \mathrm{g} of $$water at $$42.18^\circ \mathrm{C}. If $$the metal gains $$19.11 \ \mathrm{kJ} of $$energy, what is the final temperature? (Specific heat of water $$= 4.184 \ \mathrm{J/g \cdot ^\circ C})$$

$$q = m c \Delta T \rightarrow 19,110 = 615.5 \times 4.184 \times (T_f - 42.18) \rightarrow T_f = 49.6^\circ \mathrm{C}$$

Question 1

A 0.50 kg ball is dropped from a height of 10.0 m. Ignoring air resistance, what is the velocity of the ball just before it hits the ground? (Use $$g = 9.8 \ \mathrm{m/s^2$})$$

Accepted Answer

$$v = \sqrt{2gh} = \sqrt{2 	imes 9.8 	imes 10.0} = 14.0 \ \mathrm{m/s}$$

Question 2

Which of the following best describes an exothermic reaction?

Accepted Answer

A reaction that releases heat to the surroundings, causing the surroundings to feel warm.

Question 3

A 120.0 g sample of water is cooled from $$90^\circ \mathrm{C} to$$ $$45^\circ \mathrm{C}. If $$the specific heat capacity of water is $$4.184 \ \mathrm{J/g \cdot ^\circ C}$$, how much heat is released?

Accepted Answer

$$q = m c \Delta T = 120.0 	imes 4.184 	imes (45 - 90) = -22,396.8 \ \mathrm{J}$$

Question 4

Which of the following processes is endothermic?

Accepted Answer

Water boiling

Question 5

A refrigerator uses $$780 \ \mathrm{kWh} of $$electrical energy per year. How many kilocalories does it use in three years? ($$1 \ \mathrm{kWh} = 860 \ \mathrm{kcal})$$

Accepted Answer

$$780 	imes 3 	imes 860 = 2,010,600 \ \mathrm{kcal}$$

Question 6

A 15.7 g sample of silver raises its temperature by $$17.2^\circ \mathrm{C}$$ when it absorbs $$684.5 \ \mathrm{J} of $$heat. What is its molar heat capacity? (Molar mass of Ag = $$107.87 \ \mathrm{g/mol})$$

Accepted Answer

$$C_{	ext{molar}} = \frac{q}{n \Delta T} = \frac{684.5}{(15.7/107.87) 	imes 17.2} = 28.0 \ \mathrm{J/mol \cdot ^\circ C}$$

Question 7

Which of the following statements is true regarding the First Law of Thermodynamics?

Accepted Answer

Energy can be transferred between a system and its surroundings but cannot be created or destroyed.

Question 8

A gas expands from $$4.3 \ \mathrm{L} to$$ $$8.2 \ \mathrm{L} at a $$constant pressure of $$931 \ \mathrm{mmHg}. If $$the system absorbs $$2.34 \ \mathrm{kJ} of $$energy as heat, what is the change in internal energy? ($$1 \ \mathrm{L \cdot atm} = 101.3 \ \mathrm{J}$$, $$1 \ \mathrm{atm} = 760 \ \mathrm{mmHg})$$

Accepted Answer

$$\Delta E = q + w = 2,340 \ \mathrm{J} + [-(931/760) 	imes (8.2-4.3) 	imes 101.3] = 2,340 - 509 = 1,831 \ \mathrm{J}$$

Question 9

Which of the following is the correct balanced thermochemical equation for the formation of barium oxide, $$\mathrm{BaO}$$, from its elements in their standard states?

Accepted Answer

$$\mathrm{Ba}(s) + \frac{1}{2} \mathrm{O}_2(g) \rightarrow \mathrm{BaO}(s)$$

Question 10

A 50.0 g sample of heated metal is placed into 822.5 g of water at $$32.08^\circ \mathrm{C}. If $$the metal gains $$14.55 \ \mathrm{kJ} of $$energy, what was the initial temperature of the water? (Specific heat of water $$= 4.184 \ \mathrm{J/g \cdot ^\circ C})$$

Accepted Answer

$$q = m c \Delta T ightarrow 14,550 = 822.5 	imes 4.184 	imes (32.08 - T_i) ightarrow T_i = 28.6^\circ \mathrm{C}$$

Question 11

Which of the following substances will show the greatest temperature change upon absorbing $$25.0 \ \mathrm{J} of $$heat? (Given: $$c_{\mathrm{Al}} = 0.900$$, $$c_{\mathrm{Cu}} = 0.385$$, $$c_{\mathrm{C_2H_5OH}} = 2.450$$, $$c_{\mathrm{wood}} = 1.760 in$$ $$\mathrm{J/g \cdot ^\circ C}$$, all samples are $$250.0 \ \mathrm{g})$$

Accepted Answer

Copper ($$\mathrm{Cu})$$

Question 12

A chemist wishes to determine the final temperature of $$30.0 \ \mathrm{g} of a $$metal ore placed into an insulated beaker containing $$615.5 \ \mathrm{g} of $$water at $$42.18^\circ \mathrm{C}. If $$the metal gains $$19.11 \ \mathrm{kJ} of $$energy, what is the final temperature? (Specific heat of water $$= 4.184 \ \mathrm{J/g \cdot ^\circ C})$$

Accepted Answer

$$q = m c \Delta T ightarrow 19,110 = 615.5 	imes 4.184 	imes (T_f - 42.18) ightarrow T_f = 49.6^\circ \mathrm{C}$$

Question 13

If the temperature of a water bath increases from $$25 \ \mathrm{K} to$$ $$50 \ \mathrm{K}$$, what can be said about the amount of heat absorbed, assuming constant heat capacity?

Accepted Answer

It will double.

Question 14

Which of the following statements deals with potential energy with nonchemical energy associated?

Accepted Answer

A chunk of coal being thrown into a furnace to generate heat.

Question 15

A radioactive particle weighing $$7.20 	imes 10$$^{-9}$$ \ \mathrm{g} is $$found $$110 \ \mathrm{m}$$ above the earth's surface. What is its potential energy? (Use $$g = 9.8 \ \mathrm{m/s^2$})$$

Accepted Answer

$$PE = mgh = 7.20 	imes 10$$^{-12}$$ \ \mathrm{kg} 	imes 9.8 	imes 110 = 7.76 	imes 10$$^{-9}$$ \ \mathrm{J}$$

Question 16

Consider the thermochemical reaction: $$2 \mathrm{Mg}(s) + \mathrm{O}_2(g) \rightarrow 2 \mathrm{MgO}(s) \quad \Delta H = -1204 \ \mathrm{kJ}. $$How many grams of $$\mathrm{MgO}$$ are produced during an enthalpy change of $$-375 \ \mathrm{kJ}$$?

Accepted Answer

$$\frac{2 	imes 40.3}{1204} 	imes 375 = 25.1 \ \mathrm{g}$$

Question 17

Which of the following is NOT a form of mechanical energy?

Accepted Answer

Thermal energy due to random motion of molecules

Question 18

A gas reaction is allowed to take place in a canister while submerged in water at a temperature of $$25^\circ \mathrm{C}. $$The gas expands and does PV work on the surroundings equal to $$38.5 \ \mathrm{J}. At $$the same time, the temperature of the water decreases to $$20^\circ \mathrm{C} as $$the energy in the gas reaction reaches $$36.4 \ \mathrm{J}. $$What is the change in energy of the system?

Accepted Answer

$$\Delta E = q + w = 36.4 + (-38.5) = -2.1 \ \mathrm{J}$$

General Chemistry Study Notes: Thermochemistry, Energy, and Heat Capacity

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