(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 to determine the specific latent heat of fusion of ice. State two precautions necessary to obtain an accurate result.
(c) Using the kinetic theory of matter, explain why ice can change to water at 0°C without any change in temperature.
Explanation
(a) The specific latent heat of fusion of ice is \(3.4 \times 10^{5}Jkg^{-1}\) means that \(3.4 \times 10^{5} J\) of hoat energy is required to change 1kg mass of ice from solid state to the liquid state without a change in temperature.
Weigh a clean, dry copper calorimeter empty, together with stirer. Half fill the calorimeter with water previously warmed to about 8°C above room temperature and reweigh it to find the mass of water. Record the temperature of the water when it is say about 5°C above room temperature and then immediately add small pieces of ice, to the water. Stir the water until all the ice is melted before adding another piece. Continue until final temperature is 5°C below the room temperature. Record this temperature. Finally, reweigh the calorimeter to find the mass of ice melted.
Calculations: Heat gained by ice in forming water = Heat lost by water and calorimeter
\(M_{1} L + M_{1} C_{w} \theta_{1} = (M_{w} C_{w} + M_{c} C_{c}) \Delta \theta\)
\(\therefore L = \frac{(M_{w} C_{w} + M_{c} C_{c}) \Delta \theta - M_{1} C_{w} \theta_{f}}{M_{1}}\)
where \(M_{1} - \text{mass of ice}\)
\(M_{c} - \text{mass of calorimeter}\)
\(C_{w} - \text{specific heat capacity of water}\)
\(C_{c} - \text{specific heat capacity of calorimeter}\)
\(\theta_{f} - \text{final temperature}\)
\(\Delta \theta - \text{change in temperature of calorimeter and water}\)
(c) In a solid, such as ice, the molecules, which are held together by inter molecular forces, vibrate about a mean position. As ice absorbs more heat, the vibration of the molecules have enough energy to overcome the force binding them together. They are now free to move about in a random fashion as in a liquid.