Question

1. You mix 45 mL of 0.20 M HCl with 55 mL of 0.20 M KOH in a perfectly insulated solution calorimeter. The following reaction occurs:
HCl(aq) + KOH(aq) KCl(aq) + H2O(l)
The temperature of both solutions before mixing is 20.50 °C. The temperature of the solution rises to 21.69 °C after mixing. What is the enthalpy change per mole of water produced? The specific heat capacity of water and the solution is 4.2 J/g·K. Assume the density of all solutions is 1.00 g/mL.

Answer 1

HCl(aq) + KOH(aq) --------> KCl(aq) + H2O(l)

45 ml 55ml

0.2 molar 0.2 molar

0.2 × 45/1000 0.2 ×55/1000

0 0.2 ×10/1000 0.2×45/1000 0.2×45/10^3

Volume of the solution is 100 ml.

Density of the solution is 1gm/ml.

Mass of the solution(m) is 100gm.

$C=4.2J/g.K$

$Tf=294.69 K$

$Ti =293.5 K$

$Qabs by solution = m×C×change in T$

$Qabs by solution = 100g ×4.2J/g.K×1.19K$

$Qabs by solution = 499.8 J$

$Qreaction = -Qabs by solution=-499.8J$

$enthalpy change/mole of water =Qreact/moles$

$enthalpy change= -499.8 J/(0.2×45/1000)mol$

$enthalpy change= - 55.53× 10^3 J/mol$

$enthalpy change= -55.53KJ/mol$ (Ans)