How many kilojoules are released when 8.2 g of water condenses at 100°C and cools to 15°C?

Jun 2, 2016

$- 185 , 402 + \left(- 2 , 913.46\right) = - 188315.46 J$

$Q = 1.9 x {10}^{5} J$

$Q = 1.9 x {10}^{2} k J$

Explanation:

There are two steps to this thermochemistry process

First we are going to calculate the condensation process at ${100}^{o} C$.
Then calculate the cooling of the liquid from ${100}^{o} C \to {15}^{o} C$

Step 1 $Q = m {C}_{p}$

$Q = 8.2 g \left(- 2261 \frac{J}{g}\right) = - 185 , 402 J$

Step 2 $Q = m \left({T}_{f} - {T}_{i}\right) {C}_{p}$

$Q = 8.2 g \left({15}^{o} - {100}^{o} C\right) 4.18 \frac{J}{{g}^{o} C} = - 2 , 913.46 J$

$- 185 , 402 + \left(- 2 , 913.46\right) = - 188315.46 J$

$Q = 1.9 x {10}^{5} J$

$Q = 1.9 x {10}^{2} k J$