## Unit 7 Properties Of Bulk Matter Chapter 8 Change Of State Of Matter Short Answer Type Questions

**Question 1. Tea gets cooled when sugar is added to it. Why?**

**Answer:**

** Tea gets cooled when sugar is added to it. **

When sugar is added to tea, it melts. For this purpose, the required latent heat is collected by sugar from tea, thereby cooling the tea.

**Question 2. The water equivalent of a calorimeter is 10 g and it contains 50 g of water at 15 °C. Some amount of ice, initially at -10°C is dropped in it and half of the ice melts till equilibrium is reached. What was the initial amount of ice that was dropped (when specific heat of ice = 0.5 cal · g ^{-1} · °C^{-1}, specific heat of water = 1.0 cal · g^{-1} · °C^{-1} and latent heat of melting of ice = 80 cal · g^{-1})?**

- 10g
- 18 g
- 20 g
- 30 g

**Answer:**

Let, ice of m g is dropped in the calorimeter.

m x 0.5 x 10 + m/2 x 80 =60x 1 x 15

or, m = 20 g

The option 3 is correct.

**Question 3. Steam at 100°C is passed into 20 g of water at 10°C. When water acquires a temperature of 80 °C, the mass of water present will be [Take specific heat of water = 1 cal · g ^{-1} · °C^{-1} and latent heat of steam = 540 cal · g^{-1}]**

- 24 g
- 31.5 g
- 42.5 g
- 22.5 g

**Answer:**

Let m g of steam is passed into 20 g of water at 10° C.

Total heat released by the steam

= m x 540 + m( 100-80) =560/72 cal

Total heat absorbed by the water = 20(80-10) = 1400 cal

∴ 560m = 1400 or, m = 2.5 g

Now, mass of water present = 20 + 2.5 = 22.5 g.

The option 4 is correct.

**Question 4. A piece of ice falls from a height h so that it melts completely, Only one-quarter of the heat produced is absorbed by the ice and all energy of ice gets converted into heat during its fall. The value of h is [latent heat of ice is 3.4 x 15 J/kg and g = 10N/kg]**

- 544 km
- 136 km
- 68 km
- 34 km

**Answer:**

Heat produced = mgh [ m = mass of ice]

According to the question,

1/4 (mgh) = mL (L = latent heat of fusion of ice]

or, \(h=\frac{4 L}{g}=\frac{4 \times 3.4 \times 10^5}{10}=13.6 \times 10^4 \mathrm{~m}=136 \mathrm{~km}\)

The option 2 is correct.

**Question 5. A copper block of mass 2.5 kg is heated in a furnace to a temperature of 500°C and then placed on a large ice block. What is the maximum amount of ice that can melt? (specific heat of copper = 0.39 J · g ^{-1} · K^{-1}; heat of fusion of water = 335 J · g^{-1})**

**Answer:**

The ice block is at 0°C.

So the heat released by the copper block = 2500 x 0.39 x (500 – 0) = 25 x 39 x 500 J

The maximum amount m of ice would melt if the entire amount of heat released by the copper block is used up as latent heat of fusion of ice.

∴ m = \(\frac{25 \times 39 \times 500}{335}\) = 1455 g =1.455 kg

## Unit 7 Properties Of Bulk Matter Chapter 8 Change Of State Of Matter Integer Type Question And Answers

**In this type, the answer to each of the questions is a single-digit integer ranging from 0 to 9.**

**Question 1. A piece of ice (heat capacity =2100 J • kg ^{-1} • °C^{-1} and latent heat = 3.36 x 10^{5} J • kg^{-1}) of mass m g is at -5°C at atmospheric pressure. It is given 420 J of heat so that the ice starts melting. Finally, when the ice-water mixture is in equilibrium, it is found that 1 g of ice has melted. Assuming there is no other heat exchange in the process, what will be the value of m?**

**Answer:**8

**Question 2. 2 kg of ice at -20 °C is mixed with 5 kg of water 20 °C in an insulating vessel having a negligible heat capacity. Calculate the final mass (in kg) of water remaining in the container. It is given that the specific heat of water and ice are 1 kcal · kg ^{-1} · °C^{-1} and 0.5 kcal · kg^{-1} · °C^{-1} respectively while the latent heat of fusion of ice is 80 kcal · kg^{-1}.**

**Answer:**6

**Question 3. In an industrial process, 10 kg of water per hour is to be heated from 20°C to 80°C. To do this steam at 150°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 90°C. How many kg of steam is required per hour? (specific heat of steam = 1 cal · g ^{-1} · °C^{-1}, steam = 540 cal · g^{-1})**

**Answer:**1

**Question 4. A bullet of mass 10 x 10 ^{-3} kg moving with a speed of 20 m • s^{-1} hits an ice block (0°C) of 990 g kept at rest on a frictionless floor and gets embedded in it If ice takes 50% of KE lost by the system, the amount of ice melted (in grams) approximately is n x 10^{-3}. Find the value of n.(J = 4.2 J • cal^{-1}, latent heat of ice = 80 cal • g^{-1})**

**Answer:**3

## Unit 7 Properties Of Bulk Matter Chapter 8 Change Of State Of Matter Comprehension Type Question And Answers

**Read the following passages carefully and answer the questions at the end of them.**

**Question 1. An immersion heater, in an insulated vessel of negligible heat capacity brings 10 g of water to the boiling point from 16°C in 7 min. The water is replaced by 200 g of alcohol, which is heated from 16°C to the boiling point of 78 °C in 6 min 12 s, 30 g are vaporised in 5 min 6 s.**

**1. Power of heater is nearly**

- 8.4 x 10
^{3}J · s^{-1} - 84 W
- 8.4 x 10
^{3}cal · s^{-1} - 20 W

**Answer:** 2. 84 W

**2. The specific heat of alcohol is**

- 0.6 J · kg
^{-1}·°C^{-1} - 0.6 cal · g
^{-1}· °C^{-1} - 0.6 cal · kg
^{-1}· °C^{-1} - 0.6 J · °C
^{-1}

**Answer:** 2. 0.6 cal · g^{-1} · °C^{-1}

**3. The latent heat of vaporization of alcohol is**

- 854 J · kg
^{-1} - 854 x 10
^{3}J · kg^{-1} - 204 cal · g
^{-1} - 204 cal · kg
^{-1}

**Answer:** 2. 854 x 10^{3} J · kg^{-1}

**Question 2. In a physics practical examination, a student puts heat into a 500 g sample (solid) at the rate of 10 kJ · min ^{-1}, while recording its temperature as a function of time. He collects the data and plots the graph depicted. Assume no heat is lost.**

**1. What is the latent heat of fusion?**

- 35 kJ · kg
^{-1} - 70 kJ · kg
^{-1} - 25 kJ · kg
^{-1} - 30 kJ · kg
^{-1}

**Answer:** 4. 30 kJ · kg^{-1}

**2. What is the specific heat of the substance in liquid phase?**

- 1 kJ · kg
^{-1}· K^{-1} - 1.5 kJ · kg
^{-1}· K^{-1} - 6.67 kJ · kg
^{-1}· K^{-1} - None of these

**Answer:** 1. 1 kJ · kg^{-1} · K^{-1}

**3. What is the specific heat of the substance in solid phase?**

- \(\frac{4}{3} \mathrm{~kJ} \cdot \mathrm{kg}^{-1} \cdot \mathrm{K}^{-1}\)
- \(\frac{3}{4} \mathrm{~kJ} \cdot \mathrm{kg}^{-1} \cdot \mathrm{K}^{-1}\)
- \(\frac{40}{3} \mathrm{~kJ} \cdot \mathrm{kg}^{-1} \cdot \mathrm{K}^{-1}\)
- \(1 \mathrm{~kJ} \cdot \mathrm{kg}^{-1} \cdot \mathrm{K}^{-1}\)

**Answer:** 1. \(\frac{4}{3} \mathrm{~kJ} \cdot \mathrm{kg}^{-1} \cdot \mathrm{K}^{-1}\)