Calorimetry Flashcards
define thermal energy
the total internal energy of all the molecules of a substance
define heat
heat is that form of energy that flows from a hot body to a cold body when the two are kept in contact
define 1 calorie
the heat energy required to raise the temperature of 1 g of water from 14.5 C to 15.5 C
define temperature
parameter which tells us the degree of hotness or coldness of a body. it determines the direction of flow of heat when two bodies of different temperatures are kept in contact
factors affecting quantity of heat absorbed to increase temperature of a bodY
- mass of body (direct)
- increase in temperature of body (direct)
- material of body
temperature depends on
average kinetic energy of its molecules due to their random motion
define heat capacity
amount of heat energy required by a body to raise its temperature by 1 C
heat capacity C’=
amount of heat energy supplied Q/ rise in temperature t
define specific heat capacity
specific heat capacity of the substance is the amount of heat energy required to raise the temperature of unit mass of that substance by 1 C
specific heat capacity c=
= heat capacity of the body C’/ mass of the body m
= C’/ m * rise in temp
unit of specific heat capacity
J/ kg.K
relation between C’ and c
C’ = m * c
does specific heat capacity depend on mass of the body
no, does not depend on mass as it is a characteristic property of the substance of the body
specific heat capacity of good conductors of heat
low c
calorimeter
cylindrical vessel which is used to measure the amount of heat gained or lost by a body when it is mixed with another body or substance
why is calorimeter made of a thin sheet of copper
- copper is a good conductor of heat so vessel soon acquires temperature of contents
- copper has low specific heat capacity so amount of heat taken by the calorimeter itself is very low
why are outer and inner surfaces of calorimeter polished
reduce heat loss by radiation
why is calorimeter placed inside a wooden jacket
for insulation
why is space between calorimeter and wooden jacket filled with some poor conductor
to reduce heat loss by conduction
why is calorimeter covered by a wooden lid
to reduce heat loss by convection
principal of method of mixtures/ principal of calorimetry
heat energy lost by the hot body= heat energy gained by the cold body (this is based on law of conservation of energy)
m1.c1.(t1-t)= m2.c2.(t-t2)
heat energy gained by calorimeter which mixing A and B
Mass of calorimeterspecific heat capacity of its substance(t-t1)
why is climate near the sea moderate
specific heat capacity of water is very high, and of sand it is very low. Hence, the heat energy required for the same rise in temperature for water is five times of that of sand. Hence, sand gets heated or cooled more rapidly than water. This difference in temperature sets up a convection current.
why are hot water bottles used for fomentation
specific heat capacity of water is high, so it takes more time to cool down. hence, hot water bottle provides more heat energy for fomentation
why is water used as an effective coolant
water in pipes extract more heat from the surroundings, and takes a long time to heat up, because of its high specific heat capacity
water because of high specific heat capacity, imparts large amount of heat before reaching its cooling point
why is base of cooking pan made thick
mass increases, so heat capacity also increases. provides heat slowly for cooking, and keeps food warm afterwards
define change of phase
the process of change from one state to another AT A CONSTANT TEMPERATURE . it is brought about by the exchange of heat
define melting
the change from solid to liquid- on absorption of heat- at a constant temperature
the constant temperature at which a solid changes to liquid is called melting point of the solid
define freezing
the reverse change from liquid to solid- by liberation of heat- at a constant temperature
effect of pressure on melting point
- for substance which contract on melting: mp decreases by increase in pressure
- for substances which expand on melting: mp increases with increase in pressure
effect of impurities on mp
mp decreases by the presence of impurities (adding salt to ice)
define vaporisation/boiling
the change from liquid to gas- on absorption of heat- at a constant temperature
the particular temp at which vaporisation occurs is called boiling point of liquid
change in volume on BOILING
ALL liquids expand on boiling
effect of pressure on bp
increases with increase in pressure
effect of impurities on bp
increases by addition of impurities
define latent heat
heat energy absorbed or liberated in change of phase is not externally manifested by any rise or fall in temperature
specific latent heat L=
heat absorbed/liberated during phase change/ mass
define specific latent heat
L of a phase is the quantity of heat energy absorbed (or liberated) by the unit mass of the substance for the change in its phase at a constant temperature
specific latent heat of fusion of ice
heat energy required to melt the unit mass of ice at 0 C to water at 0 C without any change in temperature
specific latent heat of fusion of ice
336000 J/kg
1 kg of ice at 0 C absorbs 336000 J of heat to convert to water at 0 C
relation between 1 g of water at 0 C and 1 g of ice at 0 C
1 g of water has 336 J heat energy more than 1 g of ice
latent heat of ice
336 J /g
in cold countries, why does water in lakes does not freeze all at once
specific latent heat of fusion of ice is high. water liberates a large amount of heat to surroundings before reaching freezing point. layer of ice formed at the surface prevents loss of heat from water of the lake
