Temperature, Heat and Internal Energy

Temperature, Heat and Internal Energy

Temperature, Heat and Internal Energy

(A) Temperature and thermometers

Temperature is a measure of the hotness ofa body.

(1) Temperature scale and thermometer

Temperature is expressed using a temperature scale. A temperature scale is obtained by choosing two fixed points, and dividing the range between them into a numberof equal divisions called degrees.

The most commonly used temperature scale is the Celsius temperature scale.

Thermometer is a device for measuringtemperature. Each type of thermometer uses aphysical property that changes with temperature.For example, in a liquid-in-glass thermometer, the liquid expands and rises up in the narrow tube when temperature rises.

(2) Temperature and Particle Motion

According to the kinetic theory, all matter is made up of very tiny particles, which are constantly in motion.When they are close together, they attract/repel each other strongly. Whenthey are far apart, they hardly attract/repel each other at all.

Kinetic theory can be used to explain the general properties of solids, liquids and gases.

General property / Arrangement of particle / Movement of particles
Solids / Fixed volume and shape / Particles areclose together are arranged in fixed positions / Each particle only vibrates to and froabout a fixedposition.
Liquids / Fixed volume but no fixed shape / Particles are alsoclose together, butthey are not infixed positions. / Each particle canmove from oneplace to another.
Gases / No fixed volume and shape / Particles are veryfar apart. There isalmostno attractiveforce betweenthem. / Each particle canmove from oneplace to another.

The average kinetic energy of particles inan object increases with temperature of the object.Two bodies have thesame temperature if particles in each body have the same average kineticenergy.

(B) Heat and internal energy

When two bodies of different temperatures touch each other, energy is transferred from the hot body to the cold body until they reach the sametemperature. (The bodies are then said to be in thermal equilibrium.)

Heat is the energy transferred from one body toanother as a result of a temperature difference.

Unit of heat: joule (J)

Internal energy is the energy stored in a body. Itincreases when the temperature of the body rises,or when the body changes from solid to liquid orfrom liquid to gas.

Internal energy is the sum of kinetic andpotential energy of all particles in the body.

Unit of internal energy: joule (J)

Power means the rate of energy transfer, i.e.

Unit of power: watt (W) or joule per second (J s-1)

(C) Heat capacity and specific heatcapacity

(1) Heat capacity

Heat capacity (C) is the energy transferred toraise the temperature of the object through 1 °C.

Heat capacity = mass × specific heat capacity
or C = mc

Unit of heat capacity: J °C–1

(2) Specific heat capacity

Specific heat capacity (c) is the energytransferred to raise the temperature of 1 kg ofthe substance through 1 °C.

Energytransferred = mass × specific heat capacity × change in temperature
or E = mcT

Unit of specific heat capacity: J kg–1 °C–1

(3) Measuring specific heat capacity

Measuring specific heat capacity of water / Measuring specific heat capacity of aluminium
Experimental set-up / /
Calculation / /
Precaution / Do not switch on the heater unless its heating part is totally immersed in water.
Keep the heating part of the heater totally immersed in water throughout the experiment.
Do not take the final temperature as soon as the power supply is switched off. Stir the water and record the highest reading. / Add a few drops of oil to the holes in the aluminium block.
Place the aluminium block on a polystyrene tile.
Do not switch on the heater unless its heating part is in contact with the aluminium block.
Possible sources of error / Some energy is lost to the surroundings.
Some energy transferred is used to heat up the polystyrene cup, the stirrer and the thermometer. / Some energy is lost to the surroundings.

(4) Importance of highspecific heat capacity of water

Water is a good choice for use as a coolant.

Coastalareas have cooler summers and milder winters than inland areas of thesame latitude.

The body temperature only changes slowly when thetemperature of the surroundings changes.

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Temperature, Heat and Internal Energy