- The mixing method uses a calorimeter to measure the specific heat of a solid by observing the heat exchange until thermal equilibrium is reached.
- Heat lost by solid = Heat gained by water + Heat gained by calorimeter;
Q = Q1 + Q2 - The specific heat of the solid is calculated using known values of mass, temperature change, the specific heat of water, and the calorimeter.
Definitions [16]
Definition: Specific Latent Heat of Fusion
The amount of heat energy absorbed at constant temperature by unit mass of a solid to convert into liquid phase is called the specific latent heat of fusion.
Definition: Latent Heat of Fusion
The heat energy absorbed at constant temperature during transformation of solid into liquid is called the latent heat of fusion.
Definition: Specific Latent Heat
Specific latent heat 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.
S.I. unit of specific latent heat is J kg⁻¹, and 1 cal g⁻¹ = 4.2 × 10³ J kg⁻¹.
Definition: Latent Heat
The heat energy absorbed (or liberated) in change of phase is not externally manifested by any rise or fall in temperature, it is called the latent heat.
Definition: Boiling Point of the Liquid
The constant temperature at which the liquid transforms into gaseous state is called the boiling point of the liquid.
Definition: Melting Point of Ice
The constant temperature, at which the ice converts into water is called the melting point of ice.
Definition: Specific Latent Heat of Vapourization
The amount of heat energy absorbed at constant temperature by unit mass of a liquid to convert into gaseous phase is called the specific latent heat of vapourization.
Definition: Regelation
The phenomenon in which the ice converts to liquid due to applied pressure and then re-converts to ice once the pressure is removed is called regelation.
Definition: Anomalous behaviour of water
The behaviour of water between its temperature from 0 °C to 4 °C is called anomalous behaviour of water.
Definition: Relative Humidity
The ratio of actual mass of vapour content in the air for a given volume and temperature to that required to make the air saturated with vapour at that temperature is called the relative humidity.
% Relative humidity = \[\frac{\text{actual mass of water vapour content in the air in a given volume}}{\text{mass of vapour needed to make the air saturated in that volume}}\] × 100
Definition: Dew Point Temperature
Suppose unsaturated air at a certain temperature is taken and its temperature is decreased, a temperature is reached at which the air becomes saturated with vapour. This temperature is called the dew point temperature.
Definition: Absolute Humidity
The vapour content in the air is measured using a physical quantity called absolute humidity. The mass of vapour present in a unit volume of air is called absolute humidity. Generally absolute humidity is measured in kg/m3.
Definition: Humidity
The presence of water vapour in the air makes it moist. The moisture in the atmosphere is called humidity.
Definition: Specific Heat Capacity
The specific heat capacity of a substance is the amount of heat energy required to raise the temperature of unit mass of that substance through 1°C (or 1 K).
OR
Heat capacity of a body when expressed for the unit mass is called the specific heat capacity of the substance of that body.
OR
The amount of heat energy required to raise the temperature of a unit mass of an object by 1 °C is called the specific heat of that object.
Define heat capacity.
The heat capacity of a body is the quantity of heat required to raise its temperature by 1°C. It depends upon the mass and the nature of the body.
Definition: Principle of Heat Exchange
Heat energy lost by the hot object = Heat energy gained by the cold object. This is called as ‘Principle of heat exchange’
Formulae [2]
Formula: Specific Latent Heat
L = \[\frac{\text{heat absorbed (or liberated) for the change of phase}}{\text{mass}}\]
or
L = \[\frac {Q}{m}\]
Formula: Specific Heat Capacity
Specific heat capacity c = \[\frac{\text{Heat capacity of body } C'}{\text{Mass of the body } m}\]
or
Specific heat capacity c = \[\frac{Q}{m\times\Delta t}\]
Key Points
Key Points: Anomalous behaviour of water
- Anomalous behaviour of water refers to its contraction when heated from 0°C to 4°C, unlike most liquids that expand on heating.
- At 4°C, water attains its minimum volume and hence its maximum density.
- This behaviour is studied using Hope’s apparatus, in which temperature changes at the upper (T₂) and lower (T₁) parts of the water are recorded over time.
- As cooling begins, denser water at 4°C sinks, causing T₁ to fall rapidly, while T₂ falls more slowly.
- Once water cools below 4°C, its density decreases, causing it to rise, which in turn makes T₂ drop faster, while T₁ remains stable at 4°C briefly before decreasing.
Key Points: Unit of Heat
- SI unit of heat is Joule (J); CGS unit is calorie (cal).
- 1 cal = heat to raise 1 g of water by 1°C (14.5°C to 15.5°C).
- 1 kcal = heat to raise 1 kg of water by 1°C; 1 kcal = 1000 cal.
- The required heat may vary slightly outside the defined temperature range.
- 1 cal = 4.18 J; named after James Prescott Joule, who linked heat to energy.
Key Points: Specific Heat Capacity
- Heat energy absorbed (Q) depends on: mass (m), rise in temperature (Δt), and specific heat capacity (c), i.e., Q ∝ m × Δt × c.
- Heat capacity (C') and specific heat capacity (c) are related by: C′ = m × c.
Key Points: Measurement of Specific Heat
Important Questions [7]
- The vapour content in the air is measured using a physical quantity called ____________.
- How do we feel about air in each of the following conditions? Relative humidity is more than 60%. Relative humidity is less than 60%.
- Observe the following diagram and answer the questions given below: Specific heat capacity of metals Which element has maximum specific heat capacity? Justify. Which element has minimum specific heat
- How much heat energy is necessary to raise the temperature of 5 kg of water from 20°C to 100°C?
- Name and state the principle used to measure the specific heat capacity of a substance.
- Read the following paragraph and answer the questions based on it. If heat is exchanged between a hot and cold object, the temperature of the cold object goes on increasing due to gain of energy
- Write the use of ‘Calorimeter’.
