Chapter 5 - Heat - Calorimetry Excercise 247
What do you mean by thermal energy?
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.
Is heat a form of energy?
Yes, heat is a form of energy.
What do you understand by the term 'temperature'?
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.
Distinguish between heat and temperature.
What is the SI unit of heat and temperature?
The SI unit of heat energy is joule (J).
Define 1 joule.
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.
Which is bigger: 1 joule or 1 calorie?
1 J = 4.2 cal. So, 1 joule is bigger than 1 calorie.
Name the instrument used to measure temperature.
A thermometer is used to measure temperature.
(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.
Name the physical quantity that measures the degree of hotness.
Temperature is the physical quantity that measures the degree of hotness.
A substance is heated gradually. Does its energy increase or decrease?
Its energy increases on heating.
Why do the molecules of a gas move about freely?
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.
Name the two scales used for measuring temperature.
Two scales for measuring temperature are
i. Celsius scale
ii. Fahrenheit scale
What kind of thermometer is commonly used?
'Liquid-in-glass' kind of thermometer is commonly used.
What is the other name of Doctor's thermometer?
Doctor's thermometer is also called Clinical thermometer.
Express the melting point of ice on the Celsius scale and the Fahrenheit scale.
Which scale of temperature is commonly used and why?
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.
What is the normal body temperature of a healthy person on the Celsius scale?
The normal body temperature of a healthy person is 37oC.
Write down a relationship to convert temperature on the Fahrenheit to Celsius scale.
What are the upper and lower fixed points on the Fahrenheit scale?
Lower fixed point = 32oF
Upper fixed point = 212oF
Describe the Celsius scale of temperature.
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.
Which represents a greater temperature rise, 200C or 200 F?
Express -400C on the Fahrenheit scale.
Express 2120F on the Celsius scale.
Chapter 5 - Heat - Calorimetry Excercise 248
Express the temperature of 0 K on the:
(a) Celsius scale
(b) Fahrenheit scale
What is absolute zero?
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).
If the temperature of a body is 200C, what will be the corresponding temperature on the Kelvin scale?
Convert 370C temperature to the Fahrenheit scale.
Write the SI unit of:
(i) Amount of heat
(ii) Heat capacity
(iii) Specific Heat capacity
SI unit of:
i. Amount of heat - joule
ii. Heat Capacity - joule per Kelvin
iii. Specific Heat Capacity - joule per kilogram per Kelvin
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.
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?
Write the approximate value of specific heat capacity of water in SI unit.
Specific heat capacity of water is 4200 Jkg-1K-1.
The sp. Heat capacity of water is 4200 J kg-1 K-1. What information does this convey?
This means that 4200 J of heat is required to raise the temperature of 1kg of water by 1K.
Give one example each where high specific heat capacity of water is used (i) In cooling, (ii) As heat reservoir.
(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.
What is a calorimeter? Why is it made of copper? Give two reasons.
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.
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.
Why do the farmers fill their fields with water on a cold winter night?
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.
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?
Define the term 'heat capacity' and state its unit.
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
Define the term 'specific heat capacity' and state its unit.
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
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.)
Describe a method to determine the specific heat capacity of a solid, like a piece of copper.
Discus the role of high specific heat capacity of water with reference to climate in coastal areas.
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.
State the principle of calorimetry.
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.
Water is used as an effective coolant. Give reason.
Water is used as an effective coolant since it has a high value of specific heat capacity (4200 J kg-1K-1).