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Calorimetry

Liquid ammoni...

Question

Liquid ammonia is used in ice factory for making ice from water. If water at $20^{0} C$ is to be converted into $2 k g$ ice at $0^{0} C$ , how many grams of ammonia are to be evaporated? (Given: The latent heat of vaporization of ammonia = $341 c a l / g$ )

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Solution

Amount of heat energy released in cooling $2 k g$ water from $20^{0} C$ to $0^{0} C$ = $2 \times 1000 \times 1 \times 20 = 40000 c a l$ .

Amount of heat energy released in converting $2 k g$ water at $0^{0} C$ to ice = $2 \times 1000 \times 80 = 160000 c a l$ .

Thus, total energy required in converting water at $20^{0} C$ to ice = $40000 + 16000 = 200000 c a l$ .

Grams of ammonia to be evaporated = $\frac{200000}{341} = 586.5 g$ .

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Q. Solve the following problems:
a. Equal heat is given to two objects A and B of mass 1 g. Temperature of A increases by 3°C and B by 5°C. Which object has more specific heat? And by what factor?
b. Liquid ammonia is used in ice factory for making ice from water. If water at 20°C is to be converted into 2 kg ice at 0°C, how many grams of ammonia are to be evaporated? (Given: The latent heat of vaporization of ammonia= 341 cal/g)
c. A thermally insulated pot has 150 g ice at temperature 0°C. How much steam of 100°C has to be mixed to it, so that water of temperature 50°C will be obtained? (Given : latent heat of melting of ice = 80 cal/g, latent heat of vaporization of water = 540 cal/g, specific heat of water = 1 cal/g °C)
d. A calorimeter has mass 100 g and specific heat 0.1 kcal/ kg °C. It contains 250 gm of liquid at 30°C having specific heat of 0.4 kcal/kg °C. If we drop a piece of ice of mass 10 g at 0°C, What will be the temperature of the mixture?

Q. How much energy is required to change

2 K g

0^{0} C

20^{0} C

? (specific latent of heat of fusion of water =

3, 34, 000 J / K g

, specific heat capacity of water =

4200 J {K g}^{- 1} K^{- 1}

Q. One gram of ice at

0^{0} C

5

grams of water at

10^{0} C

. If the latent heat of ice be

80

cal/g, then the final temperature of the mixture is :

Q. A carnot engine extracts heat from water at

0^{0} C

and rejects it to room at

{24.4}^{0} C

. The work required by the refrigerator for every

1 k g

of water converted into ice (latent heat of ice

= 336 k J / k g

1

0^{\circ} C

4.6

mm Hg pressure is converted to water vapour at a constant temperature and pressure. Find

Δ H

if the latent heat of fusion of ice is

80

Cal/gm and latent heat of vaporization of liquid water at

0^{\circ} C

596

Cal per gram and the volume of ice in comparison to that of water (vapour) is neglected.

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