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EXERCISE 3 : Heat & Temperature: Concepts

Heat & Temperature: Concepts

Differences: Temperature is a measurement of the average kinetic energy of particles in an object. Heat is a flow
of energy from an object at a higher temperature to an object at a lower temperature. If you add energy as heat
to a pot of water, the water’s temperature starts to increase. Heat refers to the amount of energy in an object,
measuring the total kinetic and potential energy contained by the molecules in that object. Temperature refers to
the intensity of heat, measuring the average kinetic energy of molecules in a substance.
Effects of Heat: The important effects of heat on an object are:
Raises the temperature.
Increases volume.
Changes state.

Brings about chemical action.
Changes physical properties.
Different Units: Heat and temperature are two different but closely related concepts. Note that they have different
units: temperature typically has units of degrees Celsius ( ) or Kelvin ( ), and heat has units of energy, Joules
Units of Heat
Calories 1 cal 4.184J
Joules 1J 0.000239006 kcal / 0.000947817Btu
BTU 1 Btu 1055.06 J

The amount of heat gained or lost by a sample (q) can be calculated using the equation q=mc∆T, where m is the
mass of the sample, c is the specific heat, and ΔT is the temperature change.
Relation of Specific Heat: Specific heat is defined by the amount of heat needed to raise the temperature of
1 gram of a substance 1 degree Celsius (°C). Water has a high specific heat, meaning it takes more energy to
increase the temperature of water compared to other substances. The S.I. unit is joule per kilogram per Kelvin
(Jkg-1K-1). This quantity is known as the specific heat capacity (or simply, the specific heat), which is the heat
capacity per unit mass of a material. Experiments show that the transferred heat depends on three factors: (1) The
change in temperature, (2) the mass of the system, and (3) the substance and phase of the substance. Specific
heat capacity has two sub-classes called molar specific heat capacity at constant pressure and molar specific
heat capacity at constant volume.
Thermal Capacity: Thermal capacity is defined as the quantity of heat necessary to produce a unit change of
temperature in a unit mass of a material. Heat capacity is thus an inherent property of a substance. For example,
water has an extremely high heat capacity of 4184 J per kilogram. This implies that 4184 J of heat energy is
needed to raise the temperature of water by 1 Kelvin (or 1 Celsius). Tart with the object at a known uniform
temperature, add a known amount of heat energy to it, wait for its temperature to become uniform, and measure
the change in its temperature.
Latent Heat
Latent heat is defined as the heat or energy that is absorbed or released during a phase change of a substance.
It could either be from a gas to a liquid or liquid to a solid and vice versa. Latent heat is related to a heat property
called enthalpy. The heat of freezing is the amount of thermal energy given off as liquid freezes, and the heat of
vaporization is the amount of thermal energy that must be added to change a liquid to a gas. The SI unit of latent
heat is J/kg. The symbol of latent heat is L.
Water Equivalent: The amount of water required to consume the same amount of heat as a substance consumes
for one degree rise in the temperature is called water equivalent of a substance. It is also equivalent to the
product of the mass of the substance and its specific heat. SI unit of water equivalent of calorimeter is kilogram
i.e. Kg. Water equivalent is generally used in comparison of a water quantity. For example, Water equivalent of a
calorimeter is nothing but amount of water which will absorb same amount of heat that the calorimeter will absorb.
Water equivalent=mass x specific heat= mg x s calg-1°C-1=ms cal°C-1.

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CITS : WCS - Mechanical - Exercise 2