1. One kilogram of ice at -15 oC is heated until the whole of it evaporates. How much heat is required? Latent heat of fusion of ice = 80 cal/gm and that of steam = 540 cal/gm.
2. Calculate the energy released when (i) 20 g water at 100 °C and (ii) 20 g of steam at 100 °C are each spilt on the hand. Take the specific heat capacity of water to be 4200 J kg –1 K –1 and the specific latent heat of vaporization of water to be 2.2 MJ kg–1. Assume that the temperature of the skin is 33 °C.
3. It takes 15 minutes for an electric kettle to heat a certain quantity of water from 0 oC to the boiling point 100 oC. It requires 80 minutes to turn all the water at 100 oC into steam. Determine the latent heat of steam.
4. A refrigerator converts 60 g of water at 25 oC into ice at -30 oC in one hour. Determine the quantity of heat removed per minute. (Specific heat of ice = 0.5)
5. (i) How much heat is needed to take ice of mass m = 720 g at -10 oC to a liquid state at 15 oC? (ii) If we supply the ice with a total heat only 210 kJ, what then is the final state of the water?
6. In a cold storage ice melts at the rate of 3 kg per hour when the external temperature is 28 oC. Find the minimum power output of the motor used to run the refrigerator just to prevent melting of ice.
7. In an industrial process 10 kg of water per hour is to be heated from 20 0 C to 80 0 C.To do this, steam at 150 0 C is passed from a boiler into a copper coil immersed in water. The steam condenses in the coil and is returned to the boiler as water at 900 C. How many kg of steam is required per hour? Specific heat of steam= 1cal /gm, Latent heat of steam =540 cal/gm
8. An aluminium container of mass 100 gm contains 200 gm of ice at -200C.Heat is added to the system at the rate of 100 calories per seconds. What is the temperature of the system after 4 minutes? Specific heat of aluminium = 0.2 cal g-1(=0C)-1
9. A lead bullet at 100 0 C strikes a steel plate and melts. What was its minimum speed? Specific heat of lead =0.03, latent heat = 5cal/gm and melting point = 327 0 C. The heat produced is shared equally between the plate and the bullet.
10. An ice cube at 00C is dropped into ground and melts to water at 00C.If all the kinetic energy of the ice went into heating it, from what height did it fall?
11. When a falling hailstone is at a height of 2.0 km its mass is 2.50 g. What is its potential energy? Assuming that all of this potential energy is converted to latent heat during the fall, calculate the mass of the hailstone on reaching the ground. Take the specific latent heat of fusion of ice to be 3.36 × 105 J kg–1 and the acceleration due to gravity to be 9.81 ms–2.