Revision: Heat >> Calorimetry Physics (English Medium) ICSE Class 10 CISCE

The total internal energy of all the molecules of a substance is called its thermal energy.

The kinetic energy due to random motion of the molecules of a substance is known as its heat energy.

The measurement of the quantity of heat is called calorimetry.

The sum of the potential energy and kinetic energy of a molecule is called its internal energy.

Heat is that form of energy which flows from a hot body to a cold body when they are kept in contact.

One kilo-calorie of heat is the heat energy required to raise the temperature of 1 kg of water from 14.5°C to 15.5°C.

The temperature at which the pressure and volume of a gas theoretically reach zero is called absolute zero.

Coefficient of Linear expansion is equal to the change in length of a rod of length 1m when its temperature rises by 1°C.

Temperature is a parameter which tells the thermal state of a body (i.e., the degree of hotness or coldness of the body). It determines the direction of flow of heat when two bodies at different temperatures are placed in contact.

The heat capacity of a body is the amount of heat energy required to raise its temperature by 1°C (or 1 K).

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.

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.

OR

The amount of heat per unit mass absorbed or given out by a substance to change its temperature by one unit (one degree), i.e., 1°C or 1 K, is called specific heat capacity.

OR

The quantity of heat required to raise the temperature of a unit mass of a gas by one degree, whose exact value depends upon the mode of heating the gas and can range from zero to infinity or even be negative, is called the specific heat capacity of a gas.

The quantity of heat needed to raise the temperature of the whole body by 1°C (or 1 K) is called heat capacity.

OR

The amount of heat ΔQΔQ supplied to a substance to change its temperature from T to T + ΔT, per unit mass per unit degree change in temperature, is called specific heat:

The amount of heat required to raise the temperature of one mole of a substance through a unit degree Celsius or Kelvin is called molar heat capacity.

A calorimeter is a 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.

Calorimetry is the science of measuring heat exchange during physical or chemical processes. The word comes from the Latin calor (heat) + Greek metron (measure).

OR

An experimental technique for the quantitative measurement of heat exchange is called calorimetry.

Sublimation is the process in which a solid changes directly into a gas on heating, without passing through the liquid state.

The triple point of water is that point where water in a solid, liquid and gas state co-exists in equilibrium and this occurs only at a unique temperature and a pressure.

The process of change from one state to another at a constant temperature is called the change of phase.

OR

A transition from one state of matter (solid, liquid, or gas) to another is called change of state.

The change from solid to liquid phase by the absorption of heat at a constant temperature is called melting.

The constant temperature at which a solid changes to liquid is called the melting point of the solid.

The reverse change from liquid to solid phase with the liberation of heat at a constant temperature is called freezing and the temperature at which a liquid freezes to solid is called its freezing point. 

The particular temperature at which vaporisation occurs is called the boiling point of liquid.

The change from vapour to liquid phase on liberation of heat at a constant temperature is called condensation (or liquefaction) and the particular temperature at which the condensation occurs is called the condensation point of vapour.

The change from liquid to gas (or vapour) phase on absorption of heat at a constant temperature, is called vaporisation.

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.

OR

Latent heat is the quantity of heat energy required to change the state of unit mass of a substance from one phase to another, at constant temperature and constant pressure.

OR

The quantity of heat required to convert unit mass of a substance from its liquid state to vapour state, at its boiling point without any change in its temperature is called its latent heat of vapourization (L_v).

The quantity of heat required to convert unit mass of a substance from its solid state to the liquid state, at its melting point, without any change in its temperature, is called its latent heat of fusion (L_f).

OR

The heat energy absorbed at constant temperature during the transformation of solid into liquid is called the 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.

Heat capacity C' = \[\frac{\text{amount of heat energy supplied (Q)}}{\text{rise in temperature (Δt)}}\]

or

Heat capacity of the body C' = \[\frac {Q}{Δt}\]

C = M × c = Q/(nΔT)

Unit: J/mol · K

Specific heat capacity c = \[\frac{\text{Heat capacity of body } C'}{\text{Mass of the body } m}\]

or

Specific heat capacity c = \[\frac{Q}{m\times\Delta t}\]

Heat energy lost by the hot body = Heat energy gained by the cold body

or

m₁ c₁ (t₁ - t) = m₂ c₂ (t - t₂)

Q = m × L

where,

Q = Heat energy absorbed or released during phase change
m = Mass of the substance undergoing phase change
L = Specific Latent Heat (characteristic of the substance & process)

SI Units = J kg⁻¹

Statement: When different parts of an isolated system are at different temperatures, heat transfers from the part at higher temperature to the part at lower temperature. The heat lost by the hot object is equal to the heat gained by the cold object, provided no heat is allowed to escape to the surroundings.

(For liquid in calorimeter: m₁c₁Δθ + m_cc_cΔθ)

Key Points:

• A system is said to be isolated if no exchange of heat occurs between the system and its surroundings.
• Calorimetry literally means measurement of heat.
• Energy supplied by heater = VIt (voltage × current × time).
• This principle is based on the Law of Conservation of Energy.

• Heat is the energy that flows from a hot body to a cold body when they are kept in contact.
• The S.I. unit of heat is joule (J), while calorie and kilocalorie are commonly used units.
• One calorie is approximately equal to 4.2 joule, and kilocalorie is used to measure the energy value of foods.

• If no heat flows between two bodies in contact, they are said to be at the same temperature, even though their thermal energies may be different.
• The S.I. unit of temperature is kelvin (K), and absolute zero (0 K) is the temperature at which molecular motion ceases.

• Heat capacity (C′) of a body is directly proportional to the heat energy (Q) supplied and inversely proportional to the rise in temperature (Δt), i.e., C'​ = \[\frac {Q}{Δt}\].
• S.I. unit of heat capacity is joule per kelvin (J K⁻¹), and 1 cal K⁻¹ = 4.2 J K⁻¹.

• 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.

• A calorimeter is an insulated device used to measure heat transfer; measurement of specific heat of a substance is carried out using it.
• Principle of Calorimetry: Heat lost by hot body = Heat gained by cold body, which represents the law of conservation of heat energy.
• In the method of mixtures, a heated sample is placed in the calorimeter and the temperature change is measured to calculate specific heat using the formula Q = msΔt.
• Specific heat of a substance depends on the nature of the substance; water is preferred in calorimetry due to its high specific heat, allowing it to absorb large amounts of heat with minimal temperature change.
• For accurate results, the sample must be transferred quickly into the calorimeter and stirred well to ensure uniform heat distribution.

• The climate near the shoreline is moderate due to the high specific heat capacity of water, which causes slower heating and cooling than on land.
• Hot water bottles are used for fomentation because water does not cool quickly, thus providing more heat energy over time.
• Water is used as an effective coolant in machines because it removes more heat without a significant temperature rise.
• Farmers fill their fields with water to protect crops from frost, since water’s high specific heat capacity prevents the temperature from falling to 0°C.

• A change of state occurs when heat exchange causes a substance to transition between solid, liquid, and gas phases.
• Temperature remains constant during a phase change because heat energy changes molecular arrangement (potential energy), not molecular speed (kinetic energy).
• The heating curve has flat plateaus at the melting point (0 °C) and boiling point (100 °C) for water, with rising slopes in between.

• Most substances expand on melting, but some, like ice and bismuth, contract on melting.
• An increase in pressure decreases the melting point of substances that contract on melting (like ice), while it increases the melting point of substances that expand on melting.
• The presence of impurities lowers a substance's melting point, as seen when salt lowers the melting point of ice to form a freezing mixture.

• The boiling point of a liquid increases with pressure and decreases with a fall in pressure; this is why water boils at 120–125°C in a pressure cooker.
• At high altitudes, water boils at 100°C due to lower atmospheric pressure, making cooking difficult and slower in open vessels.
• The addition of impurities increases the boiling point of a liquid; e.g., adding salt to water raises its boiling point, aiding faster cooking.

• Formula: Q = mL. Specific latent heat L has SI unit J kg⁻¹.
• Temperature stays constant during any phase change. Heat energy goes into breaking or forming intermolecular bonds, not into raising kinetic energy.
• Latent Heat of Fusion (water): L_f = 3.33 × 10⁵ J kg⁻¹ = 80 cal/g. Heat needed to melt 1 kg of ice at 0°C.
• Latent Heat of Vaporisation (water): L_v = 22.6 × 10⁵ J kg⁻¹ = 540 cal/g. Heat is needed to convert 1 kg of water to steam at 100°C.
• L_v ≫ L_f because vaporisation requires complete molecular separation and work against atmospheric pressure during expansion.
• All latent heat values depend on atmospheric pressure. Standard values quoted at 1 atm. Increasing pressure raises the boiling point (pressure cooker effect).

• Snow on mountains does not melt all at once due to the high specific latent heat of fusion of ice (= 336000 J kg⁻¹).
• In cold countries, water in lakes and ponds does not freeze all at once because it must lose a large quantity of heat due to the high latent heat of fusion.
• Drinks cool more quickly when ice at 0°C is added than when ice-cold water is added, because ice absorbs 336 J g⁻¹ of heat energy to melt.
• When ice in a frozen lake starts melting, the surroundings become very cold because the melting ice absorbs heat from the atmosphere.
• It is colder after a hailstorm because melting ice absorbs heat from the surroundings, lowering the temperature further.