The standard heat of the reaction CaC2 (s)+5 H2O (l) -> CaO(s)+ 2CO2(g)+ 5 H2 (g

Question

The standard heat of the reaction CaC2 (s)+5 H2O (l) -> CaO(s)+ 2CO2(g)+ 5 H2 (g) is +69.36 KJ.

a. Suppose you charge 150 g of CaC2 and liquid water into a rigid container at 25 C, heat the container until the calcium carbide reacts completely, and cool the products back down to 25 C, condensing essentially all the unconsumed water. Write and simply the energy balance equation for this closed constant-volume system and use it to determine the net amount of heat (KJ) that must be transferred to or from the reactor (state which).

b. If in part (a) the term "rigid container" were replaced with "container at a constant pressure of 1 atm," the calculated value Q would be slightly in error. Explain why.

c. If you placed 1 mol of solid calcium carbide and 5 mol of liquid water in a container at 25 C and left them there for several days, upon returning you would not find 1 mol of solid calcium oxide, 2 mol of carbon dioxide, and 5 mol of hydrogen gas. Explain why not.

I found the answer for (a) to be 121.9 KJ. But I am struggling with questions (b) and (c). Could someone help me solve those questions.

Explanation / Answer

(b)

Here when the pressure is 1 atm and constant pressure, then delta H = dQ . but there will be some error because in this container there is change in volume by the reaction. that is ,6 moles of reactants given 8 moles of products.So, moles of products are high .As volume is proportional to moles, the heat energy calculated will be equal to delta H with small error.

(c)

Here you are given that 1 mol of CaC2 and 5 mol of H2O was left for several days, the reaction will not happen. This is beacuse, the given reaction has delta H = +69.36 kJ, which is positive. It means it is endothermic reaction. Unless you provide heat, the reaction will not takes place.

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