A calorimeter contains 29.0 mL of water at 15.0 C . When 1.50 g of X (a substanc
ID: 1029181 • Letter: A
Question
A calorimeter contains 29.0 mL of water at 15.0 C . When 1.50 g of X (a substance with a molar mass of 70.0 g/mol ) is added, it dissolves via the reaction X(s)+H2O(l)X(aq) and the temperature of the solution increases to 25.5 C . Calculate the enthalpy change, H, 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/(gC)], that density of water is 1.00 g/mL, and that no heat is lost to the calorimeter itself, nor to the surroundings.
Part b.
Consider the reaction
C12H22O11(s)+12O2(g)12CO2(g)+11H2O(l)
in which 10.0 g of sucrose, C12H22O11, 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.
Explanation / Answer
1) heat released (q) = m*s*DT
m = mass of water = 29*1 = 29 g
s = specific heat of water = 4.18 j/g.c
DT = 25.5 - 15 = 10.5
q = 29*4.18*10.5 = 1.273 kj
n = no of mol of x = 1.5/70 = 0.021 mol
DHsol = -q/n
= -1.273/0.021
= -60.62 kj/mol
2) C12H22O11(s)+12O2(g)12CO2(g)+11H2O(l)
n = no of mol of sucrose = 10/342 = 0.0292 mol
q = C*dT
= 7.5*22.0
= 165 kj
DE = -q/n
= - 165/0.0292
= -5.65*10^3 kj
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