Chapter 9, Problem 9.4P

The standard heat of the reaction

   $Ca{C}_2\left(s\right)+5H_{2}O\left(l\right)\to CaO\left(s\right)+2C{O}_2\left(g\right)+5H_2\left(g\right)$

is $\Delta {\hat{H}}_r^{°}=69.36kJ$.

1. Is the reaction exothermic or endothermic at 25°C? Would you have to heat or cool the reactor to keep the temperature constant? What would the temperature do if the reactor ran adiabatically? What can you infer about the energy required to break the molecular bonds of the reactants and that released when the product bonds form?
Calculate $\Delta U_t^{°}$for this reaction. (See Example 9.1-2.) Briefly explain the physical significance of your calculated value.
2. Suppose you charge 150.0g of CaC₂and 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 simplify 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).
3. If in Part (c) the term “rigid container” were replaced with “container at a constant pressure of 1 atm," the calculated value of Q would be slightly in error. Explain why.
4. 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.