A calorimeter contains 21.0 mL of water at 13.5 °C . When 2.20 g of X (a substan
ID: 1026445 • Letter: A
Question
A calorimeter contains 21.0 mL of water at 13.5 °C . When 2.20 g of X (a substance with a molar mass of 79.0 g/mol ) is added, it dissolves via the reaction x(s) + H20(1)x(aq) and the temperature of the solution increases to 27.0 Calculate the enthalpy change, A, for this reaction per mole of X. Assume that the specific heat of the resulting solution is equal to that of water [4.18 J/(g.°C)], that density of water is 1.00 g/mL, and that no heat is lost to the calorimeter itself, nor to the surroundings. Express the change in enthalpy in kilojoules per mole to three significant figures View Available Hint(s) kJ/mol Submit Part B Consider the reaction CullnO11 (s) + 1202 (g)12CO2 (g) + 11H20(1) in which 10.0 g of sucrose, C12H22011, was burned in a bomb calorimeter with a heat capacity of 7.50 kJ/°C. The temperature increase inside the calorimeter was found to be 22.0°C. Calculate the change in internal energy, E, for this reaction per mole of sucrose. Express the change in internal energy in kilojoules per mole to three significant figures. View Available Hint(s) k./molExplanation / Answer
part A
heat released in reaction(q) = m*s*DT
m = mass of water = 21.0*1 = 21 g
s = specific heat of water = 4.18 j/g.c
DT = 27-13.5 = 13.5
q = 21*4.18*13.5 = 1185.03 j
= 1.185 kj
no of mol of X reacted(n) = 2.2/79.0 = 0.028 mol
DH = -q/n
= -1.185/0.028
= -42.32 kj/mol
answer: -42.0kj/mol
part B
No of mol of sucrose burned = w/M = 10/342 = 0.029 mol
heat released(q) = C*DT
c = heat capacity of caloremeter = 7.5 kj/c
DT = 22.0 c
q = 7.5*22 = 165 kj
DE = -q/n
= -165/0.029
= -5.69*10^3 kj/mol
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