Question

A calorimeter has negligible heat capacity. When 50 ml 0.5 of a strong a strong acid HCl (at 19.6° c) is mixed with 50 ml 0.5 of a strong base KOH (at 19.6°C), the final temperature of the solution is 23.1 °C. Assume the density of solution is 1.o g/ml and its specific heat is 4.18 j/g-°C. The heat of the reaction is;

a) -2.591 kj
b) -2.701 kj
C) 2.591 kj
d) 2.701 kj
e) -1.463 kj

Answer 1

Ans: e) -1.463 KJ

Reaction is Neutralization of strong acid and strong base and is exothermic i.e.

50 ml 0.5M HCl mixed with 50 ml 0.5M KOH

Total volume of solution is 100 ml and its weight is 100g (as density of solution is 1g/ml)

Temperature difference is 23.1-19.6 = 3.5^oC

Specific heat of solution is 4.18 J g^{-1 o}C^-1 = 4.18J heat energy is absorbed by 1 g solution to raise its temperature by 1 ^oC.

But rise in temperature is 3.5 ^oC and weight of solution is 100 g,

therefore, heat released during neutralization

= heat absorbed by calorimeter + heat absorbed by solution = heat absorbed by solution

(where, heat absorbed by calorimeter = negligible ~ zero J)

As heat is released during neutralization its sign must be negative (exothermic reaction)

hence, answer is -1.463KJ