Thermal properties and temperature Flashcards
What happens when a material receives heat energy, in terms of expansion?
molecules move faster, molecules separate further. the material will expand
What happens when a material loses heat energy, in terms of expansion?
molecules move slower, molecules come close together. the material will contract
Which state of matter expands most, for the same amount of heat energy?
Why?
gases, no forces of attraction between molecules, molecules have enough energy to overcome the weak intermolecular forces
Which state of matter expands the least, for the same amount of heat energy?
Why?
solid, because the molecules cannot overcome the strong intermolecular forces holding the molecules together
If a gas and a solid are subject to the same amount of heat energy, which will expand more?
gas
What are 3 applications of thermal expansion in everyday life?
gaps in railway tracks
fitting metal tyres onto railway train wheels
bimetallic strips
thermometers
Why are there gaps in railway tracks?
because it leaves space for solids to expand into when temperature increases
How is thermal expansion used to fit metal tyres onto railway train wheels?
since the wheel is bigger than the tyre, the tyre is heated so it expands. this will make it possible for it to fit over the wheel. then it is cooled to contract.
How does a bimetallic strip work?
two different materials on either side of a strip. when it is heated, the material which expands more will expand and cause the strip to bend (vice verse for cooling)
What is the relative order of magnitudes of the expansion of solids, liquids and gases?
(least expansion) solid - liquid - gas (most expansion)
What causes an increase in internal energy?
rise in temperature of an object
In terms of molecules, what does an increase in temperature mean?
increased average kinetic energy of molecules of a substance
Define the term ‘specific heat capacity’.
the heat energy needed for a body of mass given to increase its temperature (by 1 degree)
What is the equation for specific heat capacity?
c= ∆E / m∆θ
Describe an experiment to find out the s.h.c of water.
- connect a power pack to an ammeter, voltmeter and an electric heater
- measure starting temperature and mass of water (which should be in calormeter cup, with insulating air and another metal cup)
- turn heater on and measure the current and voltage
- turn heater off after 5 min, wait and measure maximum temperature
- find the find energy using the H = VIt formula
- plug results in s.h.c formula
How do thermometers use thermal expansion?
mercury expands as the temperature increases
What happens to the temperature of a substance as it goes from a solid to a liquid?
it will increase until the melting point is reached. the temperature stays constant until the substance is a liquid.
What happens to the temperature of a substance as it goes from a liquid to a gas?
it will increase until the boiling point is reached. temperature stays constant until the substance is a gas.
Name 3 differences between boiling and evaporation.
boiling only occurs at boiling point
evaporation is much slower
evaporation is only at the surface, unlike boiling which is throughout surface
boiling forms bubbles
boiling requires an external thermal energy source
What is condensation, in terms of particles?
when a gas cools down, the particles move more slowly
they do not have the energy they had to overcome the intermolecular forces
particles get closer together and form a liquid
What is solidification, in terms of particles?
when a liquid cools down, the particles move more slowly
they do not have the energy they had to overcome the intermolecular forces
particles get closer together and form a solid
Define ‘evaporation’.
the escape of more energetic particles from the surface of a liquid
Evaporation has a ______ effect.
cooling
How does evaporation cool down a liquid?
molecules with a higher KE escape, leaving behind molecules with less KE. this causes the liquid to cool down.
What is one example of evaporation’s cooling effect in real life?
sweating
How does sweating work?
water evaporates from our skin, the temperature of the water falls, and removes heat energy from our body
What are factors that influence the rate of evaporation?
temperature
wind
surface area
How does temperature influence the rate of evaporation?
molecules move faster, can escape surface of liquid
increased temperature, increased rate of evaporation
How does wind influence the rate of evaporation?
decreases number of molecules above the liquid surface, leaving space for them
increased wind, increased rate of evaporation
How does surface area influence the rate of evaporation?
more molecules are positioned at the surface and can escape
increased surface area, increased rate of evaporation
