(a) Explain what is meant by the following statement. The specific latent heat of fusion of ice is \(3.4 \times 10^{5}Jkg^{-1}\). (b) Describe an experiment...

(a) The statement means that \(3.4\times10^{5}\,\text{J}\) of heat is required to change \(1\,\text{kg}\) of ice at \(0^\circ\text{C}\) completely into water at \(0^\circ\text{C}\), without any change in temperature.

(b) Experiment (method of mixtures):

• Half-fill a lagged calorimeter (of known mass \(m_c\) and specific heat \(c_c\)) with warm water; measure the mass of water \(m_w\) and the initial temperature \(\theta_1\).
• Dry some small pieces of pure melting ice at \(0^\circ\text{C}\) with blotting paper and drop them into the water; stir until all the ice just melts.
• Record the lowest (final) temperature \(\theta_2\), and find the mass of ice added \(m_i\) by reweighing.
• Heat lost by water and calorimeter = heat used to melt the ice + heat to warm the melted ice from \(0^\circ\text{C}\) to \(\theta_2\):

from which the specific latent heat of fusion \(L\) is calculated.

Two precautions: dry the ice thoroughly and use ice already at \(0^\circ\text{C}\); lag the calorimeter and stir gently to reduce heat exchange with the surroundings.

(c) Kinetic-theory explanation. When ice melts at \(0^\circ\text{C}\), the heat supplied is used to break down the rigid bonds of the ice lattice, increasing the potential energy of the molecules and letting them move past one another as a liquid. It does not increase their average kinetic energy. Since temperature depends on the average kinetic energy of the molecules, the temperature stays constant at \(0^\circ\text{C}\) throughout melting.