Q.3.102 - An Introduction to General, Organic, and Biological Chemistry

Question

A 115-g sample of steam at ${100}^{o}C$ is emitted from a volcano. It condenses, cools, and falls as snow at $0^{o}C$. How many kilojoules were released?

Step-by-Step Solution

Answer

$346 kJ$were released 

Step 1: Introduction

Mass of steam released is $115 g$ and specific heat of water $c=1.0\mathrm{cal}/{\mathrm{g}}^0\mathrm{C}$

After condensation of steam heat released is $540 \mathrm{cal}/\mathrm{g}$

The heat of fusion of water after condensing is $79.7 \mathrm{cal}/\mathrm{g}$

The heat released after condensation of steam =$\frac{115\times 540}{1000}=62 kcal$

The heat released after condensation of water =$\frac{115\times 79.9}{1000}=9.17 kcal$

Step 2: Explanation

Temperate change $∆T={100}^{o}C-0^{o}C={100}^{o}C$

Heat released $Q=mc\mathrm{\Delta }T$

$\Rightarrow \frac{115\times 79.7}{1000}=9.17 kcal$

The total heat released from the steam is

 $$\begin{gathered} =62 \mathrm{kcal}+11.5 \mathrm{kcal}+9.17 \mathrm{kcal} \\ =82.17 \mathrm{kcal} \\ =82.17\times 4.184 (1 kcal=4.184 J) \\ =346 kJ \end{gathered}$$