Chapter 14 - Thermal Physics Flashcards
14.1
What is Thermal Equilibrium ?
Thermal equilibrium is the net flow of thermal energy transferred of two substances in contact. One object will be cooler and the other object will be hotter. The hotter object will cool down and the cooler one will warm up, until they are at the same temperature, where there will be no net energy transfer.
Absolute scale of Temperature
Temperature is a number used to indicate the level of hotness of an object on some scale.
Celsius scale is commonly used to measure temperature. It marks the melting point of pure ice as 0°C, and the boiling point of water as 100°C, under atmospheric pressure. The
thermodynamic scale of temperature uses the triple point of pure water and is measured in kelvin (K) - also an SI unit
T(K) = T(°C) + 273.16
What does this mean
Conversion from C to K
Temperatures in K will always be positive.
As for the lowest temperature in K, it will always be 0K.
0C = 273.15K
14.2
What is a kinetic model
A kinetic model describes how all substances are made up of atoms/molecules which has arrangements that differ depending on the phase (solid liquid gas) of the substance
What is the Kinetic model of a solid?
In solids, particles are closely packed together.
There are strong electrostatic forces of attraction between molecules.
The molecules have kinetic energy, which allows them to vibrate around their fixed positions without breaking structure.
What is the kinetic model of a liquid
In the liquid phase, the particles are free to move around as they have more kinetic energy.
There is still electrostatic attraction, but it is weaker than solids.
What is the kinetic model of a gas
In the gaseous phase, the particles have the most kinetic energy, allowing them to move with a high speed in random directions.
As the particles are far apart in distance, ithas a larger volume than a liquid.
The collisions made by gas particles exert pressure on the container.
What is Brownian motion
The molecules of a gas travel in random directions with random velocity.
This is called BROWNIAN MOTION, and can be seen by looking at smoke particles in air.
The smoke particles are visible under a microscope, and exhibit random motion because of their collisions with the molecules in air, which result in a transfer of momentum in random ways.
Explain what internal energy is?
The internal energy of a substance is defined as the sum of kinetic and potential energy associated with the atoms or molecules which make up the substance
What is absolute zero (0 K)
Absolute zero is 0K, and is the point where all molecules in a substance stop moving completely.
This is also where the substance has minimal internal energy.
The internal energy here is entirely due to the electrostatic potential energy, as the molecules do not have any kinetic
energy
What happens when internal energy is increased?
For internal energy to increase, we need to increase the temperature of the substance. As temperature increases, the kinetic energy of atoms/molecules in the substance increases, therefore a greater internal energy.
What happens to the internal energy during a change in phase?
When a substance changes state, (solid to liquid) temperature stays constant and so does the kinetic energy. But potential energy changes significantly, depending on the change of state.
