Question

How much heat is needed to change 20 g of mercury at$20°C$

into mercury vapor at the boiling point?

Short answer

The answer is$Q=6.8kJ$

Step-by-step solution

Total Heat of Mercury

Temperature Change of Mercury is at the initial level of $20°C$and the maximum level of temperature is $357°C$.

Here, $Q_1$is Temperature Change and $Q_2$is phase change

Therefore, the total heat is

$Q=Q_1+Q_2$

Also, $Q_1=Mc∆T$

Thus,

role="math" localid="1649083560585" $\begin{array}{rcl}{Q}_1& =& Mc(T_2-T_1)\\ & =& 0.944\times {10}^{3}J\\ & =& 0.944kJ\end{array}$

On the other hand,$Q_2=M{L}_v$

Calculation of Result

Here $L_v$is Heat of Vaporization

Thus,$$\begin{gathered} Q_2=M{L}_v \\ =5.92\times {10}^{3}J \\ =5.9kJ \end{gathered}$$

Now,

$\begin{array}{rcl}Q& =& Q_1+Q_2\\ & =& 0.9kJ+5.9kJ\\ & =& 6.8kJ\end{array}$