Question

$\left(i\right)$ Water in lakes and ponds do not freeze at once in cold countries. Give a reason in support of your answer.
$\left(ii\right)$ What is the principle of Calorimetry?
$\left(iii\right)$ Name the law on which this principle is based.
$\left(iv\right)$ State the effect of an increase of impurities on the melting point of ice.

Answer 1

$\left(i\right)$ The specific latent heat of fusion of ice is sufficiently high $(336J$ $g^{-1})$. So to freeze water, a large quantity of heat has to be withdrawn, hence if freezes slowly.

$\left(ii\right)$ Heat energy lost by the hot body is equal to the heat energy gained by the cold body. This is called principle of calorimetry. For this, hot and cold body should be kept in close contact and there should not be any exchange of heat from surroundings.

$\left(iii\right)$ Law of conservation energy.

The law of conservation of energy states that the total energy of an isolated system remains constant. It is said to be conserved over time. Energy can neither be created nor destroyed; rather, it transforms from one form to another.

$\left(iv\right)$ The melting point of ice decreases by increase of impurities in it.

Impurities disrupt the regular arrangement of particles and hence the bonding. Thus less energy is needed to break the bonds and melting point decreases.