Bomb Calorimetry Questions 1 When you begin the experiment t

Bomb Calorimetry Questions

1. When you begin the experiment, the oval bucket will probably be dry before you fill it with water for the first calorimetric run. After that, it will be wet unless you dry it between runs as instructed. If you don’t dry it, will the heat capacity determined from the benzoic acid runs be too high or too low? Will this cause the calculated internal energy of combustion of camphor to be too large (i.e. too negative) or too small (not negative enough)?

2. When the camphor is ignited by the electrical current and the combustion occurs, the temperature is high enough that the water formed is in the gaseous state. However, you are told to use Hess\'s Law and the enthalpies of formation of CO2(g) and H2O(l) to calculate the enthalpy of formation of camphor. Why is it appropriate to use the enthalpy of formation for liquid water rather than gaseous water?

Solution

Bomb calorimeter

1. If the bucket is not dried in between the runs, the heat capacity determined for benzoic acid would be too high due to greater amount of water in the system.

This would cause the calculated internal energy of combustion of camphor to be too large.

2. The water formed at that temperature condenses in the bucket and therefore it is said to use enthalpy of formation of liquid water rather than gaseous water for calculations.