Question

CHE201-71: General Chemistry and Quantitative Analysis I laboratory: Chapter 5 Recitation 1. When 1.025 g of naphthalene (C16H) burns in a bomb calorimeter, the temperature rises from 24.25 °C to 32.33 "C. The heat capacity of the calorimeter is 5.86 kJ/"C. Calculate: a) Gran per mole of naphthalene for the combustion process b) gran per gram of naphthalene for the combustion process Instant cold packs, often used to ice athletic injuries on the field contain ammonium nitrate and water separated by a thin plastic divider. When the divider is broken the ammonium nitrate dissolved in water according the reaction: NH4NO3(8) ► NH4 (aq) + NO3(aq) When 1.25 g of NH.NO, is dissolved in 50 g of water, the temperature of the solution decrease from 25.8 °C to 21.9 °C. Assume that the specific heat of the solution is the same as that of pure water, 48 J/g °C, Calculate: a) AHan per mol of NH.NO, for the solution b) AHaxn per gram of NH.NO, for the solution c) Is the solution process exothermic or endothermic? 3. Calculate the change in internal energy (AE) of a system that releases 622 kJ of heat and does 105 kJ of work on the surrounding. Is the process exothermie or endothermic? 4. Consider the following thermochemical equation for the combustion of methane (CH), CH() 20 (g) + CO (4) 21-0 g). AH --802.3 kJ How much heat would be released by the combustion of 150.4 g of methane?

Answer 1

1.

Heat change of calorimeter

= heat capacity of calorimeter × temperatute change

= 5.86× (32.33 - 24.25)

= 47.35 KJ.

Heat change in combustion = - 47.35 KJ.

Moles of napthalene = mass/molar mass

= (1.025/128)

= 0.008

Now

a) q_rxn per mole of combustion of napthalene

= (- 47.35/0.008)

= - 5918.75 KJ/mole

b) q_rxn per gram

= - (47.35/1.025)

= - 46.28 kJ/g