Question

The following graph shows the temperature variation of pure mercury with the amount of heat energy supplied. Calculate the specific latent heat of melting (or fusion) of mercury in ${\text{cal g}}^{-1}$, if $85\text{g}$ of mercury is heated.

• A. $1$
• B. $3$
• C. $8$
• D. $5$

Answer 1

The correct option is B $3$

From the graph, the slope remains constant at $-40{}^{\circ }\text{C}$, from $0$ to $1063\text{J}$ of heat, i.e. M.P. of mercury = $-40{}^{\circ }\text{C}$
Heat energy absorbed during melting, $\text{Q}=1063-0=1063\text{J}$
Given, the mass of the mercury taken, $\text{m}=85\text{g}$
Specific latent heat of melting (or fusion), $\text{L}=\frac{\text{Q}}{\text{m}}=\frac{1063}{85}=12.5{\text{J g}}^{-1}$

$1{\text{cal g}}^{-1}=4.2{\text{J g}}^{-1}$
$⟹12.5{\text{J g}}^{-1}=\frac{12.5}{4.2}{\text{cal g}}^{-1}$$=2.9976{\text{cal g}}^{-1}\approx 3{\text{cal g}}^{-1}$