Heat (science)

# Heat:
Heat is a form of energy due to kinetic energy of vibrating molecules and it produces sensation of hotness or coldness. S.I. unit of heat is joule.
# Temperature:
Temperature is the degree of hotness or coldness of a body. Its S.I. unit is Kelvin.
# Differences between heat and temperature:


Heat    Temperature      
It is a form of energy, which gives sensation of coldness or hotness.    It is a degree of hotness or coldness of a body.      
Its S.I. unit is joule.    Its S.I. unit is Kelvin.      
It is measured by a calorimeter.    It is measured by a thermometer.      
It is the cause of change in temperature.    It is an effect of heat.      
It measures total KE of all molecules of a substance.    It measures the average KE of molecules of a body.      
It does not decide the flow of heat itself.    It decides the flow of heat as heat flows form higher to lower temperature.   
# One Calorie:
Amount of heat needed to raise temperature of 1 gm of pure water through  1o C  is called one calorie heat. Calorie is CGS unit of heat. 1 calorie = 4.2 Joule
# Effects of Heat:
Heat causes the following effects on objects
Change in temperature
Change in the volume(expansion)
Change in the state
Change in the solubility
Chemical change
# Specific heat capacity
It is the amount of heat required to raise the temperature of unit mass of that substance through 1°C or 1°k. If the specific heat capacity of any substance is more than it needs more heat to increase its temperature and it will contain more heat energy than other substances at same temperature.
Specific heat capacity of water is 4200J/kgºC. So, it can absorb large amount of heat for this reason it is used as a cooling agent.
# Example:
Calculate the amount of heat required to raise the temperature of 3 kg of water from 20°C to 40°C.
Solution:   
Given,
    Mass (m) = 2 kg.
    Initial temperature (t1) = 20°C
    Final temperature (t2) = 40°C
    Specific heat capacity (s) = 4200J/kg°C
We know the relation
    H = m x s x (T2 - T1)
 Substituting the values
    H = 2 × 4200(40 - 20)
       = 4800 × 20
       = 16800 Joules.  (Hence, 16800 Joules of heat is required.)

# Anomalous expansion of water
Generally any substances increase its volume on heating. But, if water at 0°C is heated its volume will decrease till its temperature is 4°C and after that its volume will increase 5°C onwards. Due to its least volume at 4°C it will have maximum density at that temperature.
                         Due to this property, water bodies in cold regionstarts freezing from the top layers. It helps for the existence of aquatic plants and animals.





Q] When we get out of the bed on a very cold morning, we feel air  of ht room cold, but when we come back staying  outside for sometimes, we feel air of the room warm , why?
Ans] When we get out of the bed on a very cold morning, we feel air  of ht room cold, but when we come back staying  outside for sometimes, we feel air of the room warm because heat always flows form high temperature to lower temperature. In fact, when we get out of the bed, our body surface temperature is higher than air temperature of the room. Therefore, heat flows from the body to the air and we feel cold. When we come back to the same room, the situation is just opposite. Our body surface temperature is lower than that of air temperature, therefore, heat flows form the air to our body and we feel warm.

Q] During high fever a wet cloth is kept on the forehead of the patient, why?
Ans] During high fever a wet cloth is kept on the forehead of the patient, because heat always flows from high temperature to low temperature. Therefore, the wet cloth is kept in order to reduce the high temperature due to fever as the heat flows form the body to the wet cloth.

Q] Water in an earthen pot remains cold in summer
Ans] Water in an earthen pot remains cold in summer, because water gets evaporated coming out from a large number of small pores of the pot. The heat lost by water molecules for the evaporation makes inside eater cool.

# Reasonable Facts:
When a red hot iron nail is plunged into boiling water, heat flows for the iron nail to the nail to the water. Here, the amount of heat is more in eater than the red hot iron nail, but the iron nail is at higher temperature than that of water. Hence, heat always flows from high temperature to low temperature.

 When water at 0oC is heated, its volume decreases up to 4oC and begins to increase after 4oC only. This unusual     behavior of water is known as anomalous expansion of water.

When a beaker completely filled with water of 4oC is heated or cooled, water overflows because of the anomalous expansion of water. The volume of water increases even when temperature falls (becomes cool) and as usual the volumes rise with rise in temperature.

Water taps may burst at very cold night in Himali region, because of the anomalous expansion of water. The volume of water trapped at 4oC is minimum due to which on further cooling to 0oC, ice made from water gets expanded. It gives outward pressure and the pipe may burst.

Aquatic animals can stay alive even in a frozen pond because of the anomalous expansion of water. In fact, the density of water of 4oC becomes maximum and sinks to the bottom. On further cooling to 3oC, 2oC,1oC, the water forms a successive layer. Finally, water at 0oC changes into ice, while aquatic animals remain safe at 4oC below the ice layer.

The amount of heat needed to raise the temperature of 1kg of a substance through 1oC(or 1K) is known as specific heat capacity. Its SI unit is Jkg-1oC-1.The quantity of heat supplied (Q) to a Q = ms dt where, s is specific heat capacity

Specific heat capacity of some substance is more. The substances having more specific heat capacity need more heat to raise their   temperature.

Specific heat capacity of water is 4200Jkg-1oC-1. It means, in order to raise the temperature of 1 kg water through  1oC, 4200J of heat should be supplied.

As the specific heat capacity of water is very high, it is used for cooling hot engines as well as for heating system. Higher the value of specific heat capacity, higher will be the amount of heat absorbed by the body. Therefore, it is used for cooling hot engines, because it can absorb large amount of heat of the engines. Similarly, large quantity of heat may be available by cooling hot water and it is suitable for heating purpose.

A key made up of aluminum is colder than that of iron, because specific heat capacity of aluminum is higher than that of iron. Due to this reason, equal amount of heat available to both leads to fewer rises in temperature of the aluminum key. Therefore, it becomes colder than the iron key.

Sea breeze occurs at day and land breeze occurs at night, because specific heat capacity of land (of soil) is less than that of water. During daytime the temperature of the land becomes higher than that of the sea due to the heat of the sun. It makes the pressure of air reduced. Therefore, air blows from land to sea. Due to this reason sea breeze occurs at days and land breeze occurs at night.

# Specific heat capacity of some materials:

S.N.    Materials    In Jkg-1oC-1      
1.    Mercury    138      
2.    Copper     380      
3.    Iron    470      
4.    Sand    800      
5.    Aluminum    910      
6.    Air    993      
7.    Ice    2100      
8.    Paraffin oil    2200      
9.    Water    4100   
# Exercise for Practice:
Define a calorie? What effects would have been seen in the life of aquatic organisms in the very cold regions if water hadn't shown anomalous expansion of water? Explain your answer.
The specific heat capacity and mass of the two substances A and B are shown in the given table. Which substance will get more heated if they are heated equally? Give reason.   


Matter    Mass    Sp. Heat Capacity      
A    1 Kg    390      
B    1 Kg    380   

What is mean by specific heat capacity of mercury is 138 Joule per kg°C? Write down the cause that the night of desert is very cold and day of that place is very hot.   
What is the temperature of water at the bottom of a pond when its surface water freezes? Explain with reasons.   
Define the term 'heat'. If heat is supplied to a solid continuously, it melts. Give reason to this.   
Mention any two effects of heat. Calculate the Sp. Heat capacity of water if 2 kg water at 25°C required 2.1 × 105J heat energy to increase its temperature to 50°C.   
Define specific heat capacity. If 10 kg water is heated from 50°C to 100°C, how much heat is required for it?   
A glass tumbler cracks when hot water is poured in it. Why?   
Give a difference between heat and temperature.   
Explain why a beaker full of water at 4°C overflows if the temperature is decrease or increased.   
Aquatic animals can survive in a pond in a cold region even though the outer surface of the pond is frozen. Mercury is heated faster than water. Why?   
Give the concept of heat and temperature on the basis of molecules.
What is meant by specific heat capacity? How much heat is required to raise the temperature of 150 gm of lump of iron from 25°C to 15°C.?    (Specific heat capacity of iron = 480J/kg°C)
What do you mean by the specific hat capacity of water is 4200J/kg°C. Write down the cause that the night of desert is very cold and day of that is very hot.   
Write down the cause of using water to cool the engine of motor car.
Due to winter season the temperature of water is 5°C. If 20 liters of water has to be heated to 35°C for taking bath. Calculate the amount of heat required for it. (The specific heat capacity of water is 4200J/kg°C and the mass of 1 liter of water is 1 kg)   
    Heat capacity of 1000 Joules is released while a lump of iron of mass 2 kg at 90°C is cooled to 15°C. Calculate the specific heat capacity of iron.   
Write two effects of heat with an example of each.
Why do ice made of water float in it? Why water is called anomalous liquid?   
Calculate the amount of heat required to raise the temperature of a frying pan by 80°C if the mass of the pan is 0.5 kg and its specific heat capacity is 480J/kg°C.