Physics Unit 1: Heating Processes
Chapter 1
There are various forms of energy e.g., potential energy, kinetic energy, thermal energy.
Potential: has the potential to do work
Kinetic: energy of motion, doing work
Heat is energy in the process of being transferred from one place to another due to the temperature difference. It can be defined as the transfer of thermal energy (Q)
Heat is thermal energy doing work
The kinetic particle model of matter suggests that matter is made up of particles that are constantly moving.
States of matter include solids, liquids and gases.
Higher temperature = faster molecular movement
Objects can be considered to have their energy as two types: macroscopic energy and microscopic energy.
Macroscopic: energy of bulk
Microscopic: energy of atomic level
Internal energy, U, is the total microscopic kinetic and microscopic potential energy of the particles in a system.
Thermal energy consists of microscopic kinetic energy and potential energy stored within/between bonds
Change in internal energy of a system equals the change in thermal energy.
Temperature is a measure of the average kinetic energy of the particles in a system.
Kinetic energy is directly related to the temperature of the system. A change in temperature is due to the addition or removal of thermal energy from a system.
Temperature is measured in °F, °C and K.
°C = K + 273
Absolute zero is the temperature at which all particle motion stops.
Absolute zero = 0K or -273°C
Heating a substance causes it to expand due to the increased speed of the particles or the increased vibrations within and between the particles themselves.
Different substances expand at different rates.
In Thermal physics, Microscopic energy = internal energy = thermal energy
Thermal energy consists of microscopic kinetic energy + micro potential energy with/between bonds
Particle motion can be vibrational, rotational, translational
Translational = moving up and down
Chapter 2 Specific Heat Capacity
0th law thermodynamics: transfer of energy from a system with higher temperature to a system with lower temperature will occur until thermal equilibrium is reached.
The specific heat capacity (c) of a substance is the quantity of heat required to raise the temperature of 1 kg of the substance by 1°C. It is measured in J/kg/K.
The quantity of energy (Q) transferred to or from a substance is given by the equation: ΔQ = mcΔT
where Q is the energy in joules, m is the mass of the substance in kg, c is the specific heat capacity in J/kg/K, and ΔT is the change in temperature in Kelvjn/Celsius.
In a closed system, the thermal energy lost by one object is equal to the thermal energy gained by the other. This is conservation of energy.
When two bodies have the same temperatures as a third body, then the two also have temperature equal to each other.
To bring about a change of state requires energy (latent heat).
The energy required to change 1 kg of a substance from a solid to a liquid without change in temperature is called the specific latent heat of fusion (Lf).
The energy required to change 1 kg of a substance from a liquid to a gas without change in temperature is called the specific latent heat of vaporisation (Lv).
Q = mLf, where Lf is the specific latent heat of fusion measured in J/kg
As Q increases → molecular vibration speed increases (kinetic energy)
Chapter 3 Latent Heat
Remember, temperature is a measure of average kinetic energy
Q increases → kinetic energy increases
when kinetic energy exceeds melting/boiling point, phase changes
during a phase change, Q gained goes to disrupting molecular bonds, increasing the potential energy of molecules, not kinetic
Kinetic energy does not change, → Temperature has not changed
as ice melts, temperature of water remains 0 degrees as kinetic energy didn’t change
Latent heat of vaporisation: liquid ←→ gas
Latent heat of fusion: liquid ←→ solid
To calculate Q needed for a temperature change that has a phase change in between it, first find the Q needed to increase up to the phase change, then use latent heat equation to find latent heat energy required, then find Q needed to increase to final temperature
Q = mL
Q = energy
m = mass in kg
L = specific latent heat capacity