Question 2 2C2H6 (g) + 7O2 (g) 4CO2(g) + 6H2O (g) H = -1560 kJ How many grams of

Question

Question 2

2C2H6 (g) + 7O2 (g) 4CO2(g) + 6H2O (g) H = -1560 kJ How many grams of ethane (30.07 g/mol) need to react to produce 482 kJ of heat? (Give your answer as a positive number, since you cannot release negative energy.)

Question 3

2 N2(g) + O2(g) 2 NO2(g)

In a cylinder with a moveable piston (pressure remains constant) the above reaction occurs. If both the temperature drops and the volume decreases during the reaction, what are the signs of q and w?

(Note: This note is not necessary to solving this problem. Please ignore it if it does not make sense to you. For those who know a little about gas laws, the volume change here is mainly due to going from 3 moles of gas in the reactants to 2 moles of gas in the products. While the temperature change does have an effect on the volume change, it is not the main factor.)

Question 7

A piece of copper and a piece of gold of the same mass and at the same temperature of 80°C are dropped into seperate beakers each containing 100.0 g of water at room temperature. Once they equilibrate, you find that the beaker with the sample of copper is warmer than the beaker with the sample of gold. Which metal has the larger specific heat capacity?

Explanation / Answer

Answer:2) Given balanced combustion reaction,

2C2H6 (g) + 7 O2 (g) -----------> 4CO2 (g) + 6H2O (g)

Heat energy released on complete combustion i.e. H = – 1560 kJ

Stoichiometry of reaction says,

Complete combustion of 2 moles of Ethane (C2H6) 1560 kJ heat release.

Molar mass of ethane (C2H6) = 30.07 g/mol.

Hence 2 moles of ethane (C2H6) = 2 x 30.07 = 60.14 g.

It means,

60.14 g Ethane (C2H6) 1560 kJ heat release.

Or

             1560 kJ heat release 60.14 g Ethane (C2H6)

Then, 482 kJ heat release say ‘M’ g Ethane (C2H6)

By cross multiplication method we write,

M x 1560 = 60.14 x 482

M x 1560 = 28987.48

M = 28987.48/1560

M = 18.582 g

18.562 g of Ethane (C2H6) will release 482 kJ heat energy on complete combustion.

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