Q9 of 17 Page 71

Solve the following problems:

Liquid ammonia is used in ice factory for making ice from water. If water at 20oC is to be converted into 2 kg ice at 0oC, how many grams of ammonia are to be evaporated?


(Given: The latent heat of vaporization of ammonia= 341 cal/g)

Given: Latent heat of vapourisation of Ammonia =341 cal/g


The amount of heat supplied to raise the temperature will be given as:


Q = mcΔT


⇒ Q = 2kg × 1C/°-g× 20° C


⇒ Q = 2000 g×1C/°-g × 20 cal/g


⇒ Q = 40,000 cal


Now, let “m” be the amount of ammonia to be evaporated to do. Then, heat gained by ice will be:


Q = m’L


⇒


⇒ m’ = 117 g


∴ 117 grams of ammonia should be evaporated.


More from this chapter

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8

Read the following paragraph and answer the questions.

If heat is exchanged between a hot and cold object, the temperature of the cold object goes on increasing due to gain of energy and the temperature of the hot object goes on decreasing due to loss of energy.


The change in temperature continues till the temperatures of both the objects attain the same value. In this process, the cold object gains heat energy and the hot object loses heat energy. If the system of both the objects is isolated from the environment by keeping it inside a heat resistant box (meaning that the energy exchange takes place between the two objects only), then no energy can flow from inside the box or come into the box.


i. Heat is transferred from where to where?


ii. Which principle do we learn about from this process?


iii. How will you state the principle briefly?


iv. Which property of the substance is measured using this principle?

 9

Solve the following problems:

Equal heat is given to two objects A and B of mass 1 g. Temperature of A increases by 3oC and B by 5oC. Which object has more specific heat? And by what factor?

 9

Solve the following problems:

A thermally insulated pot has 150 g ice at temperature 0oC. How much steam of 100oC has to be mixed to it, so that water of temperature 50oC 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)

 9

Solve the following problems:

A calorimeter has mass 100 g and specific heat 0.1 kcal/ kg°C. It contains 250 gm of liquid at 30°C having a specific heat of 0.4 kcal/kg°C. If we drop a piece of ice of mass 10g at 0°C, What will be the temperature of the mixture?