A calorimeter contains 19.0 mL of water at 11.5 C . When 1.90 g of X (a substanc
ID: 951338 • Letter: A
Question
A calorimeter contains 19.0 mL of water at 11.5 C . When 1.90 g of X (a substance with a molar mass of 53.0 g/mol ) is added, it dissolves via the reaction X(s)+H2O(l)X(aq) and the temperature of the solution increases to 29.5 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.
Explanation / Answer
X(s) + H2O(l) X(aq)
mass of solution = 1.9+19 = 20.9 grams
q released = m*s*DT
= 20.9*4.18*(29.5-11.5)
= 1.572 kj
No of mol of X = 1.9/53 = 0.036 mol
DHrxn = 1.572/0.036 = 43.67 kj
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