Part A Use standard enthalpies of formation to calculate the standard change in
ID: 1054038 • Letter: P
Question
Part A Use standard enthalpies of formation to calculate the standard change in enthalpy for the melting of ice. (The Delta H_f for H_2O(s) is -291.8 kJ/mol). Express your answer using two significant figures. Part B Use this value to calculate the mass of ice required to cool 325 mL of a beverage from room temperature (25.0 degree C) to 0.0 degree C. Assume that the specific heat capacity and density of the beverage are the same as those of water. Express your answer using two significant figures.Explanation / Answer
1. Hf° = standard heat of formation
Hf°reaction = Hf° products - Hf° reactants
if the reaction is H2O (s) ----> H2O(l)
Hf°reaction = Hf° liquid water - Hf° ice
Hf°reaction = -285.8 kJ/mole - (-291.8 kJ/mole) = 6.0 kJ/mole
2. heat gained by ice melting = heat lost by cooling beverage
(mass x Hf°) ice = (mass x Cp x dT) beverage
mass ice = (mass x Cp x dT) beverage / (Hf°) ice
mass ice = 325 mL x 1.00 g/mL x 4.18 J/gC x (25-0 C) / 6000 J/mole
= 5.66 mole ice
= 5.66 mole x 18.0 g /mole = 101.88 g