Question

A calorimeter that measures an exothermic heat of reaction by the quantity of ice that can be melted is called an ice calorimeter. Consider a reaction in which 0.00400 mol of methane gas, CH4 (g), is burned completely at constant pressure in the presence of excess air. The heat liberated from the reaction melted 10.7 g of ice at 0 degrees celcius (the heat required to melt the ice (heat of fusion) is 333.5 J/g). What is the change in enthalpy for this reaction?

Answer 1

Ans. Total amount of absorbed by ice = Mass of ice melt x heat of fusion of ice

                                                = 10.7 g x (333.5 J/ g)

                                                = 3568.45 J

# The heat released from CH₄ combustion is absorbed by ice that further causes its melting.

So, amount of heat released during combustion = Amount of heat absorbed by ice

Or, amount of heat released during combustion of CH₄ = 3568.45 J

# Total amount of heat released per mol = Amount of heat released / Moles of CH₄ burnt

                                                = 3568.45 J / 0.0040 mol

                                                = 892112.5 J/ mol

                                                = 892.1125 kJ/ mol

Therefore, enthalpy change for the reaction, combustion of CH₄ = - 892.1125 kJ/ mol

Note: The negative sign indicates that energy is released during the process.