6. Natural gas, or methane, is an important fuel. Combustion of one mole of meth

Question

6. Natural gas, or methane, is an important fuel. Combustion of one mole of methane releases 802.3 kilojoules of energy. How much energy does that represent in kilocalories? A. 192 × 10-1 kcal B. 1.92 x 102 kcal C. 3.36 × 103 kcal D. 1.92 x 10 kcal E. 3.36 x 10 kcal , as a pioneer, you wished to warm your room by taking an object heated on top of a pot-bellied stove to it, which of the following 15-pound objects, each heated to 100°C, would be the best choice? The specific heat capacity (in J/(g K) for each substance is eiven in parentheses.Iron (0.450), copper (0.387), granite (0.79), gold (0.129), water (4.18) 7. If, A. iron B. copper C. granite D. gold E. water 8. Benzene is a starting material in the synthesis of nylon fibers and polystyrene (styrofoam) Its specific heat capacity is 1.74 J/(g K). If 16.7 kJ of energy is absorbed by a 225-g sample of benzene at 20.0°C, what is its final temperature? A. B. C. D. E. -22.7°C 36.7°C 42.7°C 62.7°C none of these choices is correct 9. A piece of copper metal is initially at 100.0°C. It is dropped into a coffee cup calorimete containing 50.0 g of water at a temperature of 20.0°C. After stirring, the final temperatur of both copper and water is 25.0°C. Assuming no heat losses, and that the specific heat (capacity) of water is 4.18 J/(gK), what is the heat capacity of the copper in J/K? A. 2.79 J/K B. 3.33 J/K C. 13.9 J/K D. 209 J/K E. none of these choices is correct

Explanation / Answer

6.

1 cal = 4.184 Joules

1 J = 1 / 4.84 cal

So,

802.3 kJ = 802.3 / 4.184

= 1.92 * 102 kcal

(B)

7.

(D) Gold. because it has lower specific heat.

8.

heat change = mass * specific heat * change in temperature

16700 = 225 * 1.74 * (t2 - 20.0)

t2 - 20.0 = 42.6

t2 = 62.6

(D)

9.

Total heat change = 0

50.0 * 4.184 * (25.0 - 20.0) + C * (25.0 - 100.0) = 0

1046 - 75.0 * C = 0

C = heat capacity of copper = 13.9 J/K

(C)

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