Question

In a coffee-cup calorimeter, 100.0 g of H2O and 100.0 mL of 1M HCl are mixed. The HCl had an initial temperature of 44.6 C and the water was originally at 24.6 C. After the reaction, the temperature of both substances is 31.3 C.
Required:
a. Was the reaction exothermic or endothermic? Explain.
b. Calculate how much heat the water lost or gained.

Answer 1

Answer:

Exothermic reaction for the HCl, endothermic reaction for the water

$2803.28\ \text{J}$

Explanation:

Heat was lost by HCl as its temperature lowered, so it was an exothermic reaction for the HCL.

Heat was gained by water as its temperature increased, so it was an endothermic reaction for the water.

m = Mass of water = 100 g

c = Specific heat of water = $4184\ \text{J/kg}^{\circ}\text{C}$

$\Delta T$ = Change in temperature of water = $(31.3-24.6)^{\circ}\text{C}$

Heat is given by

$Q=mc\Delta T\\ =0.1\times 4184\times (31.3-24.6)\\ =2803.28\ \text{J}$

Heat gained by water is $2803.28\ \text{J}$.