Question

The amount of heat needed to melt $2kg$ of ice at its melting point, when latent heat of ice is $80cal/g$, is _____.
$(1cal=4.184J)$

• A. $40\times {10}^{5}J$
• B. $6.7\times {10}^{5}J$
• C. $3.35\times {10}^{5}J$
• D. $1.675\times {10}^{5}J$

Answer 1

The correct option is B $6.7\times {10}^{5}J$

Latent heat of ice is defined as the amount of heat needed to convert 1g of ice into water. As given in the question, its value is $80cal/g$.

Since $1cal=4.184J$
$80cal/g=80\times 4.184J/g$
$=334.72J/g$

Heat needed to melt $2kg$ of ice is:
Heat = mass $\times$ latent heat of ice
$=2\times 334.72kJ$
$=669.44kJ$
$=669.44\times {10}^{3}J=6.7\times {10}^{5}J$