Nature of heat (caloric, kinetic theory etc.}

Question 1

What is the caloric theory of heat ?

Answer 1

An obsolete theory of the 18th century. It was believed that heat was an invisible fluid called ‘caloric’, which would combine with matter and cause temperature to rise

Question 2

State two argument for the caloric theory

Answer 2

1. Objects expand when heated because the increased ‘caloric’ they contain causes them to occupy more space
2. Heat flows from hotter to cooler bodies because ‘caloric’ particles repel each other

Question 3

State three arguments against the caloric theory

Answer 3

1. The weight of a body should increase when heated, because it should then contain ‘caloric’. However the weight remains the same.
2. When bodies are heated so that they change state (solid to liquid or liquid to gas), an increase in ‘caloric’ cannot be detected
3. When different materials are given the same amount of heat (‘caloric’), their temperatures increase by different amounts, indicating that they receive different quantities of ‘caloric’

Question 4

What was Rumford’s cannon-boring experiment against the caloric theory?

Answer 4

He realized that the heat energy transferred when a cannon was being bored was inexhaustible and depended only on the work done in boring the hole. The ‘caloric’ theory was therefore not possible; if ‘caloric was a material substance, there would be a time when all of it left the cannon

Question 5

The kinetic energy states that

Answer 5

The particles of matter (atoms, molecules) are in constant motion of vibration, translation or rotation. The kinetic energy they possess is responsible for their temperature.

There is space between the particles. Forces (bonds) pull them together when they are near to each other, and so the particles have potential energy

When a substance is heated, the heat energy supplied could result in an increase in the kinetic energy of the particles of the substance, and hence its thermal energy, causing the temperature to rise

When a substance is heated so that it changes state, the heat energy supplied results in an increase in the spacing of the particles and hence an increase in their potential energy, allowing them to break bonds with their neighbors and to expand against any surrounding pressure

Question 6

What theory replaced the caloric theory ?

Answer 6

Kinetic theory

Question 7

Differentiate between the caloric and kinetic theories of heat as they existed in the 18th century

Answer 7

In the caloric theory heat was believed to be an invisible fluid ‘caloric’, which could combine with matter and raise its temperature while the kinetic theory states that when a substance is heated, the heat energy supplied could result in an increase in the kinetic energy of the particles of the substance, and hence in its thermal energy, causing the temperature to rise.

Question 8

Define theory

Answer 8

An intelligent explanation about some phenomenon

Question 9

Discuss the role of Joule’s experiments in establishing the principle of conservation of energy.

Answer 9

Joule’s experiment concluded that the potential energy of the masses was transformed to kinetic energy of the paddles which then transformed to thermal energy of the water, causing the temperature to rise.

Question 10

Define brownian motion

Answer 10

Brownian motion is the random, uncontrolled movement of particles in a fluid as they constantly collide with other molecules.

Question 11

In the kinetic theory energy will flow from a (1)________ object to a (2)________ one.

Particles in the cold object will (3)_____ kinetic energy, whereas particles in the hot object will (4)_____energy

Answer 11

1. hotter
2. colder
3. gain
4. lose

Question 12

TRUE/FALSE

Energy will continue to flow until both objects reach the same temperature

Answer 12

TRUE