Heating Processes Flashcards
What is energy
The ability to do work
Energy makes things happen
- Work is what happens
Measured in Joules
What is conservation of energy
Energy cannot be created or destroyed, can only be transferred or transformed
What is the points of kinetic particle model
1) All matter is made up of particles
2) Particles are constantly moving
3) Particles are attracted to eachother
4) Particles have elastic conditionsW
What is the bonds between particles of different states of matter
Solid - very strong
Liquid - strong
Gas - very weak
What is temperature
Average kinetic energy of all particles in a substance
Can use Celsius or Kelvin
What is absolute zero
Lowest temperature
No particle movement
Unattainable (Impossible)
What is internal energy
Total energy of all particles in a substance
Heat = Transfer of internal energy (Q)
What is kinetic energy
Particle motion / vibration
More kinetic energy = Motion of particles give more temperature
What is potential energy
Particle separation / bonding
Separating particles changes state from solid-liquid-gas
Why doesn’t temperature change during changing state
Energy goes into increasing particle separation to change state
No extra movement when heating = No extra temperature
What happens during normal heating state of substance
Energy goes into increasing particle movement
Extra movement = Change in temperature
What is first law of thermodynamics
If heat added to system or work done on system = Internal energy rises
If heat removed from system or work done by system = Internal energy drops
Formula for internal energy
Difference(U) = Q + W
What is thermal expansion
Whenever substance heated, it expands
- Increase in temperature = Vibrate with more kinetic energy, move further apart
- Least noticeable in solids
What is specific heat capacity
Heat energy needed to raise temperature of 1 kg of metal by 1 degree celsiusW
What is the proportionality of specific heat capacity
Greater the mass of substance, greater the energy required to heat substance
- Q proportional to m
The more heat transferred to substance, them ore the temperature of substance increases
- Q proportional to Different(T)
Specific heat capacity is constant of proportionality
What is equation of specific heat capacity
Q = m * c * Difference(T)
What is latent heat
Energy required to change state of 1kg of material at constant temperature
When substance changing state, temperature remains the same
What is equation of latent heat
Q = mL (L either fusion or vaporisation)
What is difference between latent heat vs specific heat capacity
Latent heat is during changing state (Potential energy)
Specific heat capcacity during normal heating phase, temperature is increasing (Kinetic energy)
What is latent heat of fusion (Melting)
Thermal energy transferred to solid = Temperature increases
- Particles within solid gain internal energy, faster vibration
Solid at melting point, particles move further apart, reducing strength of bonds
- Temperature doesn’t increase, energy transformed into potential energy, reducing intermolecular forces
What is latent heat of vaporisation (Boiling)
Thermal energy transferred to liquid = Temperature of liquid increases
- Particles within liquid gain internal energy, faster vibration
Liquid at boiling point, particles move further apart, reducing strength of bond
- Temperature doesn’t increase, energy transformed into potential energy, reducing intermolecular forces
Which latent heat requires more energy and why
More energy to convert from liquid to gas than solid to liquid
- As intermolecular forces need to be fully broken
Therefore latent heat of vaporisation
How does evaporation & cooling work
Occurs at all temperatures, as not all particles have same kinetic energy
- If near the surface, can escape attractive forces
- Loss of particles = Average kinetic energy lowered, lower temperature
What is thermal equilibrium
Two systems undergo energy transfer until they are the same temperature
Changes of state may occur
Ideal situation, no heat loss to environment
What is the general equation for heat loss
Heat lost by hot object = Heat gained by cold object
What is power (Heating processes sense)
Rate at which energy transferred to reach thermal equilibrium (By heat or work)
- 1 Watt = 1 Joule / Second
Power (W) = Energy (J) / Time (s)
What is conduction
Transfer of heat from one location to another, without matter changing location
- Must be touching to occur
- Transferred via particle collisions or free electrons
- Most easily in solids
What are the factors affecting thermal conduction
Nature of material (Conductivity)
Temperature difference between the two objects (Higher temperature difference = Faster energy transfer)
Thickness of material (Thicker = More collisions need to occur)
Surface area (Higher surface area = Higher number of particles involved in transfer process)
What are conductors
Materials that pass on heat energy well (Eg. Metals)
What are insulators
Materials that can’t pass on heat energy well (Eg. Styrofoam)
What is convection
Transfer of heat via convection currents
- Possible, as density of fluids are dependent on temperature
Fluids heated, expands, becomes less dense & rises
Cold & more dense fluids move downwards to take its place = Flow
What are the factors that affect thermal convection
Temperature difference between heat source and convective fluid
In container, the placement of source of heat
What is radiation
Object above absolute zero emits heat energy through radiation (Electromagnetic waves)
Radiation can travel through space (Doesn’t require medium)
What can happen when radiation hits an object
Reflected (Bounced off object)
Transmitted (Passed through object)
Absorbed (Transfer of heat energy)
What is emissivity
Ability to emit thermal radiation
Some surfaces better at reflecting & absorbing infrared radiation
What are the factors that affect thermal radiation
Surface area (Larger exposed area, higher rate of radiant transfer)
Temperature difference (Higher difference = Higher rate of radiant transfer)
Surface colour and texture (Determine if surface will emit / absorb radiant energy)
Which surfaces are good at absorbing & reflecting infrared radiation
Dark colours best at absorbing & radiating heat
Light colours worst at absorbing & radiating heat
What is efficiency
Measure of how much energy is retained, when moving from system to system
Is the % of input energy that produces useful output
What is equation for efficiency
( (Useful Energy or Energy Output ) / Energy Input ) * 100%
