Latent Heat Answers

Latent Heat

Latent Heat of fusion of ice = 3.36 x 10⁵ J kg^-1

Latent Heat of vaporization of water = 2.25 x 10⁶ J kg^-1

Specific heat capacity of water = 4200 J kg^-1 K^-1

1. How much heat energy is needed to change 0.010 kg of water at 20^oC to steam at 100^oC?                    25860J
2. How much heat energy is needed to change 0.020 kg of ice at 0°C into steam at 100°C?           60 120J  
3. How much heat energy is needed to melt 0.010 kg of ice at 0^o C and then heat the water formed to 20^o C? 4200j
4. What mass of ice at 0 °C is needed to cool 0.086 kg of water from      54 °C to 6 °C?                     .048kg
5. When a kettle boils a space can be seen between the spout and the so called `cloud of steam'. If your finger were placed in the space a much more serious scald would result than if it were placed in the `cloud of steam'. Explain why, and criticize the expression `cloud of steam'.
6. A heating coil takes 14 min to heat 0.20 kg of water from 20 °C to boiling point. How much longer will it take to boil away 0.02 kg of the boiling water?     562.5s
7. A 1 kW immersion heater takes 225 s to boil away 0.1 kg of water at 100 °C. Find the specific latent heat of vaporization of water.                     2.25x 10⁶ J kg^-1
8. How long will it take an immersion heater of power 500 W to boil away a mixture of 0.05 kg of water and 0.02 kg of ice initially at 0 °C? 387 s
9. A mixture of ice and water at 0 °C contains 0.060 kg of ice. A 750 W immersion heater takes 26.8 s to melt all the ice. Deduce a value for the specific latent heat of fusion of ice.        336000J kg^-1
10. A mixture of ice and water at 0 °C has a total mass of 1 kg, and con­tains 0.5 kg of ice. An immersion heater melts all the ice in 168 s, and then needs a further 84 s to heat the mixture to 20 ^°C. Find the specific latent heat of fusion of ice.            336000 Jkg^-1
11. A vessel of heat capacity 115 J K^-1 contains 0.30 kg of water and 0.20 kg of ice at 0 °C. An immersion heater takes 134.4 s to melt the ice and a further 88.6 s to heat the vessel and its contents to 20 °C. Find the specific latent heat of fusion of ice. 336000 Jkg^-1
12. A heating coil takes 115 s to heat 0.05 kg of a liquid from 20 °C to its boiling-point of 80 °C. It needs a further 340 s to boil away 0.02 kg of the liquid. If the specific heat capacity of the liquid is 2300 J kg^-1 K^-1, find its specific latent heat of vaporization. 1.02 x 10⁶ Jkg^-1