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Flashcards in Thermal physics Deck (47)
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Define temperature

a measure of the average kinetic energy of the particles in a system


Define heat

the flow of thermal energy


Define thermal equilibrium

when two objects are at the same temperature so there is no flow of heat.


What causes pressure?

The collisions between gas particles and the inside walls of the container


What are the properties of an ideal gas

1. Molecules move with random motion, 2. Molecules obey Newton’s laws, 2. Molecules have same average kinetic energy, 3. There are no attractive forces between molecules, 4. Collisions between molecules are elastic, 5. Molecules are point masses (have zero volume), 6. Time taken between collisions is much greater than during collisions.


Describe Brownian motion

particles moving randomly due to collisions with many other small, fast particles.


State the third law of thermodynamics

the entropy of an ideal substance will be zero at absolute zero (0K).


What is Avogadro’s constant?

The number of atoms in exactly 12g of carbon-12 (6.02x1023)


What is the specific latent heat of fusion?

The energy needed to change the state a substance from solid to liquid without a change of temperature.


What is the specific latent heat of vaporisation?

The energy needed to change the state a substance from liquid to gas without a change of temperature.


Define empirical

Based on observation or experience rather than theory or pure fact.


What is meant by the term elastic collisions?

Both KE and momentum are conserved and total E is constant before and after the collision


Define absolute scale

Measured in K starting at absolute zero


Particles exert pressure on the wall of a container because…

Molecules have momentum
Momentum change at wall
Momentum change at wall leads to force


Why is average velocity in a container zero?

Velocity is a vector
random direction
velocities cancel



a chemical process where a solid becomes a gas without going through a liquid stage


What is the difference between heat and temperature?

Heat is the flow of thermal energy as it flows from a high temperature to a low whereas temperature is a measure of the kinetic energies of the particles in a selected substance.