A 3.25 g sample of Zn(s) is added to a constant-pressure calorimeter containing

Question

A 3.25 g sample of Zn(s) is added to a constant-pressure calorimeter containing 200.0 g of HCl(aq) and reacts completely with the excess HCl(aq) according to the chemical equation: Zn(s) + 2HCl(aq) rightarrow ZnCl_2 (aq) + H_2 (g) The solution is initially at a temperature of 20.95 degree C and reaches a temperature of 30.10 degree C by the end of the reaction. Calculate delta H degree for this reaction using the data given and assuming that the HCl (aq) solution is pure water (s (H_2 O) = 4.184 J/g- degree C).

Explanation / Answer

q = mass * Cwater * delta T

= (3.25 + 200) * 4.184 * (30.10-20.95)

delta H = 7781.14 J = -7.781 kJ( minus because reaction is exothermic)

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