Calorimeter Important Questions

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Very Short Answers Questions [1 Mark Questions]

Ques. Calorimeters are generally made up of

1. Aluminium
2. Copper
3. Zinc
4. Brass

Ans. The correct answer is b. Copper

Explanation: A calorimeter is a device that measures the specific heat of a substance. Because copper is a good heat conductor with a low specific heat capacity, it is the most appropriate material for making calorimeters. Because of its low specific heat capacity, it quickly reaches equilibrium temperature by absorbing heat.

Ques. The specific heat capacity of copper is

1. 0.1 J g^-1 K^-1
2. 0.2 J g^-1 K^-1
3. 0.3 J g^-1 K^-1
4. 0.4 J g^-1 K^-1

Ans. The correct answer is d. 0.4 J g^-1 K^-1

Explanation: Copper has a specific heat capacity of 0.4 J g^-1 K^-1. This indicates that we need to provide 0.4 J of energy to raise the temperature of one gram of copper by one degree Celsius.

Ques. Water is used to cool the radiators of engines, because

1. Of its lower density
2. It has a high specific heat
3. It is easily available
4. It is cheap

Ans. The correct answer is b. It has a high specific heat

Explanation: Due to the large specific heat of water, it absorbs a large amount of heat with a very small temperature charge.

Ques. How much heat energy is gained when 5 kg of water at 20 ℃ is brought to its boiling point

1. 1680 kJ
2. 1700 kJ
3. 1740 kJ
4. 172 kJ

Ans. The correct answer is a. 1680 kJ

Explanation: Heat gained by the water is given by

Q = mass of water x specific heat of water x change in temperature

⇒ Q = 5 x 4.2 x 1000 x (100 - 20)

⇒ Q = 1680 x 10³ J or 1680 kJ

Ques. 2 g of the steam condenses when passed through 40 g of water initially at 25 ℃. The condensation of steam raises the temperature of water to 54.3 ℃. What is the latent heat of steam

1. 536 cal/g
2. 540 cal/g
3. 480 cal/g
4. 270 cal/g

Ans. The correct answer is b. 540 cal/g

Explanation: Let L be the latent heat and using the principle of calorimetry

2L + 2(100 - 54.3) = 40 x (54.3 - 25.3)

⇒ L = 540.3 cal/g

Ques. It is difficult to cook rice in an open vessel by boiling it a high altitudes because of

1. High boiling point and low pressure
2. Low boiling point and high pressure
3. High boiling point and high pressure
4. Low boiling point and low pressure

Ans. The correct answer is d. Low boiling point and low pressure

Explanation: With the rise in altitude, the pressure and the boiling point decrease.

Ques. The amount of heat required to raise the temperature of a body through 1 K is called its

1. Entropy
2. Specific heat
3. Water equivalent
4. Thermal capacity

Ans. The correct answer is d. Thermal capacity

Explanation: The amount of heat required to raise the temperature of a body through 1 K is called its thermal capacity.

Ques. A metallic ball and a highly stretched spring are made of the same material and have the same mass. They are heated so that they melt, the latent heat required

1. Is greater for the ball
2. Is greater for the spring
3. Are the same for both
4. The two may or may not be the same depending upon the metal.

Ans. The correct answer is c. Are the same for both

Explanation: The latent heat is independent of the configuration. Ordered energy spent in stretching the spring will not contribute to heat which is disordered kinetic energy of molecules of substance.

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Short Answers Questions [2 Marks Questions]

Ques. What is a calorimeter?

Ans. Calorimeters are instruments used to measure the heat capacity of materials generated during reactions, whether physical, chemical, or mechanical. It is designed to determine thermal changes that occur during a reaction.

Ques. What is meant by calorimetry?

Ans. The method of measuring the amount of heat released or absorbed during a chemical reaction is known as calorimetry. The change in heat can be used to determine whether a process is exothermic (releases heat) or endothermic (absorbs heat).

Ques. What is the principle of calorimetry?

Ans. According to the principle of calorimetry, the total heat loss by an object at a higher temperature is equal to the total heat gained by the object at a lower temperature i.e.

Heat Lost = Heat Gained

Ques. What are the main components of a calorimeter?

Ans. A normal calorimeter consists of a thermometer attached to a metal vessel filled with water suspended above a combustion chamber.

Ques. What is meant by specific heat capacity?

Ans. The specific heat capacity of a substance is defined as the amount of heat required to raise the temperature of one gram of substance through one degree Celsius.

The unit of specific heat capacity is J kg^-1 ℃^-1 or cal g^-1 ℃^-1

Ques. What is the formula for heat transfer?

Ans. Heat gain or loss on a substance is directly proportional to the mass of the substance and the temperature change. It is given by the formula

Heat transfer, Q = mcΔT

Where

• m is the mass of the substance
• c is the specific heat capacity of the substance
• ΔT is the change in temperature

Ques. What are the components of a bomb calorimeter?

Ans. Bomb calorimeters are used to calculate the energy change that happens during a reaction precisely. A bomb calorimeter is made up of a small cup to hold the sample, oxygen, a stainless steel bomb, water, a stirrer, a thermometer, a dewar or insulating container (to prevent heat from the calorimeter from escaping to the surroundings), and an ignition circuit connected to the bomb.

Ques. Define thermal capacity.

Ans. The physical quantity that is used to measure the amount of heat needed to raise the temperature of a given substance is known as thermal capacity or heat capacity.

It is defined as the amount of heat required to raise the temperature of a substance through 1 ℃.

Ques. Why specific heat capacity of water is highest among all the substances?

Ans. The specific heat of water is 1 cal g^-1 ℃^-1 or 4186 J kg^-1 ℃^-1. This means that water can absorb a lot of heat without much change in its temperature. That is why the ocean and sea are known as storehouses of heat energy. For the same reason, water is used as a cooling agent in the radiators of automobiles.

Ques. Define the latent heat of a substance.

Ans. The amount of heat required to change the state of a substance without any change in its temperature is known as the latent heat of the substance.

Ques. Define the latent heat of fusion.

Ans. The amount of heat required to convert the unit mass of a substance from its solid state to its liquid state at its melting point without any change in its temperature is known as the latent heat of fusion.

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Long Answers Questions [3 Marks Questions]

Ques. Three bodies of the same material and having masses m, m, and 3m are at temperatures 40 ℃, 50 ℃, and 60 ℃ respectively. If the bodies are brought in terminal contact, what will be the final temperature?

Ans. Let m₁, m₂, and m₃ be the masses of the three bodies respectively, and T₁, T₂, and T₃ be their temperatures.

Given

• m₁ = m
• m₂ = m
• m₃ = 3m
• T₁ = 40 ℃
• T₂ = 50 ℃
• T₃ = 60 ℃

According to the principle of calorimetry, 

the heat lost by the bodies = heat gained by the bodies

(m₁s₁T₁ + m₂s₂T₂ + m₃s₃T₃) = (m₁s₁ + m₂s₂ + m₃s₃)T

Where s₁ = s₂ = s₃ = s is the specific heat capacity of the bodies, and T is the final temperature.

On substituting the values, we get

 (ms x 40 + ms x 50 + 3ms x 60) = (ms + ms + 3ms)T

⇒ T = 270/5 = 54 ℃

Ques. What are the applications of calorimeters?

Ans. Calorimeters are very important in everyday life. Calorimeters are used to manage the metabolic rates of the human body while also maintaining the temperature of the body. The calorimeter is a significant component of thermodynamics since it is used to measure the heat of a process.

Calorimeters are used in a variety of thermodynamic applications in thermal industries, with the most common types of calorimeters used in everyday life being the bomb calorimeter and the coffee-cup calorimeter.

• A reaction calorimeter is used to monitor the heat generated by the sensors in reactors.
• A constant-pressure calorimeter can also be used to detect enthalpy change.
• The adiabatic calorimeter can be used to measure or analyze runtime reactions.

Ques. What are the different types of calorimeters?

Ans. The following are the different types of calorimeters

• Adiabatic Calorimeters: It is a calorimeter that indicates a runaway reaction. Because of the adiabatic environment, heat generated by the fabric test sample will cause the sample to expand due to the increase in temperature, intensifying the reaction.
• Bomb Calorimeters: A bomb is a constant-volume calorimeter that measures the heat of combustion of a particular reaction. 
• Differential Scanning Calorimeters: The differential scanning calorimeter facilitates heat transfer into the test sample, which is enclosed within a compact aluminum capsule
• Isothermal Titration Calorimeter: For an isothermal titration calorimeter, the heat of the reaction is determined using a titration experiment.

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Very Long Answers Questions [5 Marks Questions]

Ques. 100 grams of ice at 0 ℃ is mixed with 200 grams of water at 40 ℃. Calculate the final temperature of the mixture.

Ans. The heat energy required to melt ice at 0 ℃ to water at 0 ℃ is known as latent heat of fusion of ice (L) i.e.

L = 80 cal g^-1

The heat required to melt 100 g of ice = L x 100 = 80 x 100 = 8000 calories

Let the final temperature of the mixture be T.

The heat required to raise the temperature of 100 grams of water at 0 ℃ to T ℃, H = mass x specific heat of water x rise in temperature

But the specific heat of water = 1 cal g^-1 ℃^-1

⇒ H = 100 x 1 x (T - 0) = 100T

Total heat energy gained by ice, H_Gained = heat required to melt 100 g of ice + heat required to raise the temperature

⇒ H_Gained = (8000 + 100T) cal

Heat lost by 200 grams of water at 40 ℃ to T ℃, H_Lost = mass x specific heat of water x fall in temperature

⇒ H_Lost = 200 x 1 x (40 - T) = 200(40 - T) cal

According to the principle of calorimetry

H_Gained = H_Lost

⇒ (8000 + 100T) = 200(40 - T)

⇒ T = 0

Ques. Calculate the increase in the temperature of water which falls from a height of 100 m. Assume that 90% of the energy due to fall is converted into heat and retained by water.

Ans. The potential energy of the water at height h is given by

P.E = mgh

Where

• m is the mass of the water
• g is the acceleration due to gravity
• h is the height of the water

Given that 90% of the energy due to fall is converted into heat and retained by water, therefore

Useful energy that is converted into heat, Q = 90% of mgh = 0.9 mgh

⇒ Q = 0.9 x m x 9.8 x 100 = (882 x m) J …(i)

Now specific heat of water, c = 4200 J kg^-1 ℃^-1

Also, heat gained by the water is given by 

Q = mcΔT

Where ΔT is the temperature change.

⇒ Q = m x 4200 x ΔT …(ii)

Equating equation (i) and (ii), we get

882m = m x 4200 x ΔT

⇒ ΔT = 0.20 ℃

Ques. 19 grams of water at 30 ℃ and 5 grams of ice at -20 ℃ are mixed together in a calorimeter. What is the final temperature of the mixture? Given the specific heat of ice = 0.5 cal g^-1 ℃^-1 and the latent heat of fusion of ice = 80 cal/gram.

Ans. Given

• Specific heat of ice, s_ice = 0.5 cal g^-1 ℃^-1 
• Latent heat of fusion of ice, L_ice = 80 cal/gram

Specific heat of water, s_water = 1 cal g^-1 ℃^-1 

Here ice will absorb heat while hot water will release it.

Let T be the final temperature of the mixture.

Assuming the water equivalent of the calorimeter to be neglected.

Heat given by water, Q₁ = mass of water x s_water x change in temperature (ΔT)

⇒ Q₁ = 19 x 1 x (30 - T) = 570 - 19T

Heat absorbed by ice, Q₂ = m_ice x s_ice x [0 - (-20)] + m_iceL_ice + m_ices_water(T - 0)

⇒ Q₂ = (5 x 0.5 x 20) + (5 x 80) + (5 x 1 x T)

⇒ Q₂ = 450 + 5T

According to the principle of calorimetry, Q₁ = Q₂

⇒ 570 - 19T = 450 + 5T

⇒ T = 5 ℃

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