Thermal Properties And temperatures Flashcards
Thermal expansion
When solids/liquids/gases are heated, they expand
This expansion happens because the molecules start to move around (or vibrate) faster, which causes them to knock into each other and push each other apart
MOLECULES REMAIN THE SAME SIZE, they move away from each other (thats why it becomes bigger)
When temperature is increased (at constant pressure);
Solids will tend to expand the least, due to the strong intermolecular bonds
Gases expand the most, due to the very weak intermolecular bonds
Liquids fall in between the two
Uses of thermal expansion
Liquid in a thermometer rising due to temperature
A bimetallic strip has two metal strips glued together one of these metals expands more for each degree this causing the bimetallic strip to curve as its heated this movement can act as a electrical switch
Internal energy
A rise in the temperature of an object increases its internal energy by increasing the kinetic energy of all its particles
Internal energy
- potential and kinetic energy of the objects particles
Specific heat capacity definition
How much heat that is needed to heat the object by 1 degree
Different objects have different specific heat capacity’s depending on
If it has a low specific heat capacity it means it takes less heat to heat it up by one degree
Specific heat equation
Q=mcT
Q = change in thermal energy (j)
m = mass (kg)
c = specific heat capacity (joules/kg °C)
T - change in temp (°C)
Example question - Water of mass 0.48 kg is increased in temperature by 0.7 °C. The specific heat capacity of water is 4200 J / kg °C.
Calculate the amount of thermal energy transferred to the water
0.48kg x 0.7 °C x 4200 J/kg °C = 1411.2
Melting and boiling
The substance does not change temperature when its changing its state
The melting and boiling points of pure water are known as fixed points
- Ice melts at 0 °C
- Pure water boils at 100 °C
Boiling
- when you heat the water the temp rises until it boils
- at boiling point even if u add more heat it water doesn’t get hotter this means that internal energy is not rising
- the heat goes to overcoming intermolecular forces so the water can turn into gas
Melting
- when you heat ice the temp rises until it starts to melt
-at melting point even if u add more heat the ice doesn’t get hotter this means that the internal energy is not rising
- the goes to overcoming the intermolecular forces so the water can turn into liquid
Condensation and solidification (freezing)
Condensation- gas to liquid
- this is when the gas cools down and loses kinetic energy (particles don’t move as much)
- this means they cant overcome intermolecular forces so the particles get closer and only have enough energy to flow over one another
Solidification
- this is when the liquid cools down and loses kinetic energy (particles don’t move as much)
- this means they cant overcome intermolecular forces so the particles get closer and only have enough energy to vibrate
Evaporation
Evaporation occurs when more energetic molecules moving near the surface of the liquid have enough energy to escape
- The average energy of the liquid is reduced
- Therefore liquids are cooled down by evaporation
The process of evaporation can be used to cool things down:
If an object is in contact with an evaporating liquid, as the liquid cools the solid will cool as well
Factors that affect the rate of evaporation
- Increased temperature increases the kinetic energy of the molecules in the liquid
Molecules with more energy are more likely to overcome the intermolecular forces holding them in the liquid state and escape the surface
Therefore higher temperature leads to a higher rate of evaporation
-Molecules only escape the intermolecular forces of attraction at the surface of the liquid
Therefore a larger surface area leads to a higher rate of evaporation
-Air movement carries away the water vapour which has just evaporated
This dries the air and allows more water molecules to escape
Therefore increasing air movement (when indoors this is sometimes called draughts) increases the rate of evaporation
Boiling vs evaporation
Evaporation
- can happen at any temp
- can only happen from the surface
Boiling
- only boiling point
- throughout the liquid
Bimetallic strip, thermal expansion
When two equal length different types of metals are riveted together
They have lots of uses such as a fire alarm
