## Chapter 5.1 - Calorimetry Exercise 233

Question 1
What do you mean by thermal energy?
Solution 1
Thermal energy is energy that is powered by a heat source. For e.g.: an electric heater generates thermal energy that can be used to warm a cold room in the winter.
Question 2
Name the physical quantity that measures the degree of hotness.
Solution 2
Temperature is the physical quantity that measures the degree of hotness.

Question 3
A substance is heated gradually. Does its energy increase or decrease?
Solution 3
Its energy increases on heating.
Question 4
Why do the molecules of a gas move about freely?
Solution 4
Gas molecules have very weak or no bonds at all and the spaces between gas molecules are very large. So, the molecules of a gas move about freely.

Question 5
Name the two scales used for measuring temperature.
Solution 5
Two scales for measuring temperature are
i.    Celsius scale
ii.    Fahrenheit scale
Question 6
What kind of thermometer is commonly used?
Solution 6
'Liquid-in-glass' kind of thermometer is commonly used.

Question 7
What is the other name of Doctor's thermometer?
Solution 7
Doctor's thermometer is also called Clinical thermometer.
Question 8
Express the melting point of ice on the Celsius scale and the Fahrenheit scale.
Solution 8 Question 9
Which scale of temperature is commonly used and why?
Solution 9
Celsius scale and Fahrenheit scale are two commonly used scales of temperature because the former is based on the freezing point of water as 0oC and boiling point of water as 100oC. The same points on the Fahrenheit scale are 32oF and 212oF.
Question 10
What is the normal body temperature of a healthy person on the Celsius scale?
Solution 10
The normal body temperature of a healthy person is 37oC.

Question 11
Write down a relationship to convert temperature on the Fahrenheit to Celsius scale.
Solution 11 Question 12
Is heat a form of energy?
Solution 12
Yes, heat is a form of energy.

Question 13
What are the upper and lower fixed points on the Fahrenheit scale?
Solution 13
Lower fixed point = 32oF
Upper fixed point = 212oF
Question 14
Describe the Celsius scale of temperature.
Solution 14
In Celsius scale, melting point of ice and boiling point of water are referred as "lower fixed point" and "upper fixed point" respectively. The temperature difference between the reference points is divided into 100 divisions and each division is called "one degree Celsius" (1oC). Thus, the melting point of ice is taken as 0oC and the boiling point as 100oC.

Question 15
Which represents a greater temperature rise, 200C or 200 F?
Solution 15 Question 16
Express -400C on the Fahrenheit scale.
Solution 16 Question 17
Express 2120F on the Celsius scale.
Solution 17 Question 18
What do you understand by the term 'temperature'?
Solution 18
Temperature is a physical property that quantitatively expresses the common notions of hot and cold. It is the degree of hotness or coldness of a body or environment.

Question 19
Distinguish between heat and temperature.
Solution 19 Question 20
What is the SI unit of heat and temperature?
Solution 20
The SI unit of heat energy is joule (J).

Question 21
Define 1 joule.
Solution 21
1 joule is the amount of heat required to raise the temperature of 1 kg of a substance, that has specific heat capacity 1J/kgK, through 1oC.
Question 22
Which is bigger: 1 joule or 1 calorie?
Solution 22
1 J = 4.2 cal. So, 1 joule is bigger than 1 calorie.

Question 23
Name the instrument used to measure temperature.
Solution 23
A thermometer is used to measure temperature.
Question 24
(i) Plot a graph taking oC on the Y-axis and the corresponding oF along the X-axis.
(ii) Plot a graph taking oF along the Y-axis and the corresponding oC on the X-axis.
Solution 24 ## Chapter 5.1 - Calorimetry Exercise 234

Question 1
Express the temperature of 0 K on the:
(a) Celsius scale
(b) Fahrenheit scale
Solution 1 Question 2
What is absolute zero?
Solution 2
Absolute zero is the temperature at which volume or pressure of an ideal gas becomes nil. It is 0 degrees on the Kelvin scale, which translates to -273oC (or -459.4oF).

Question 3
If the temperature of a body is 200C, what will be the corresponding temperature on the Kelvin scale?
Solution 3 Question 4
Convert 370C temperature to the Fahrenheit scale.
Solution 4 Question 5
Write the SI unit of:
(i) Amount of heat
(ii) Heat capacity
(iii) Specific Heat capacity
Solution 5
SI unit of:
i.    Amount of heat - joule
ii.    Heat Capacity - joule per Kelvin
iii.    Specific Heat Capacity - joule per kilogram per Kelvin
Question 6
A bucket contains 8 kg of water at 250 C. 2 kg of water at 800 C is poured into it. Neglecting the heat energy absorbed by the bucket, calculate the final temperature of water.
Solution 6 Question 7
What mass of a liquid A of specific heat capacity 0.84 J K-1 and at a temperature 400C must be mixed with 100 g of a liquid B of specific heat capacity 2.1 J g-1 K-1 and at 200C, so that final temperature of mixture becomes 320C?
Solution 7 Question 8
Write the approximate value of specific heat capacity of water in SI unit.
Solution 8
Specific heat capacity of water is 4200 Jkg-1K-1.

Question 9
The sp. Heat capacity of water is 4200 J kg-1 K-1. What information does this convey?
Solution 9
This means that 4200 J of heat is required to raise the temperature of 1kg of water by 1K.
Question 10
Give one example each where high specific heat capacity of water is used (i) In cooling, (ii) As heat reservoir.
Solution 10
(i) In cooling - Water is used in the cooling systems of automobiles and other engines.
(ii) As heat reservoir - In cold countries, water is used as a reservoir for wine and juice to avoid their freezing. The reason is that water can provide more heat to the bottles due to its high specific heat capacity. Hence, they do not cool down further to freeze.

Question 11
What is a calorimeter? Why is it made of copper? Give two reasons.
Solution 11
A calorimeter is a device used to measure the quantity of heat transferred to or from an object.
It is made of copper because:
i.    Copper is a good conductor of heat so it attains the temperature of its contents in a very short time.
ii.    It has low specific heat (390 Jkg-1K-1). Therefore, it will take only a very little part of the heat energy given out in the experiment.
Question 12
A piece of iron of mass 2.0 kg has a thermal capacity of 966 J/0C. Find: (i) Heat energy needed to warm it by 150C, and (ii) Its specific heat capacity in SI unit.
Solution 12 Question 13
Why do the farmers fill their fields with water on a cold winter night?
Solution 13
Farmers fill their fields with water on a cold winter night to protect the crops from frost. In the absence of water, if on a cold night the temperature of the surroundings fall below 00C, then the veins of the plants shall freeze. Due to anomalous expansion of water, ice shall occupy more volume than water. As a result of this expansion, veins shall burst and crops shall be destroyed. But water sprinkled on the crops shall not allow the temperature of the veins to fall below 00C.
Question 14
The temperature of 600 g of cold water rises by 150C when 300 g of hot water at 500C is added to it. What was the initial temperature of the cold water?
Solution 14 Question 15
Define the term 'heat capacity' and state its unit.
Solution 15
Heat capacity of a body is the quantity of heat required to raise its temperature by 1oC. It depends upon the mass and the nature of the body.
Units: J/oC or calorie/oC
Question 16
Define the term 'specific heat capacity' and state its unit.
Solution 16
Specific heat capacity is the amount of heat required to raise the temperature of 1 kg of the substance by 1oC.
Units: j/kgK or calorie/g oC

Question 17
0.5 kg of lemon squash at 300C is placed in a refrigerator which can remove heat at an average rate of 30 Js-1. How long will it take to cool the lemon squash to 50C?(Sp. heat capacity of lemon squash = 4200 J kg-1 oC-1.)
Solution 17 Question 18
Describe a method to determine the specific heat capacity of a solid, like a piece of copper.
Solution 18 Question 19
Discus the role of high specific heat capacity of water with reference to climate in coastal areas.
Solution 19
The specific heat capacity of water (4200 J Kg-1 K-1) is about five times as that of sand. Due to which water takes long time to get heated up and equally long time to get cooled. Thus, large temperature difference between the land and the sea causes formation of land and sea breezes.
Question 20
State the principle of calorimetry.
Solution 20
Principle of Calorimetry:
When a hot body is mixed or kept in contact with a cold body, there is a transfer of heat from hot body to cold body such that
Total heat gained by colder body = Total heat lost by the hot body,
if there is no loss of heat to the surroundings.

Question 21
Water is used as an effective coolant. Give reason.
Solution 21
Water is used as an effective coolant since it has a high value of specific heat capacity (4200 J kg-1K-1).