IGCSE Coordinate Science 1Thermal Energy

P5, P6, C6 Key Notes

Review

• List the three major states of matter & brainstorm everything you can remember about each one.

Expansion

• Many substances expand when heated• When heated, the particles (atoms or

molecules) in a substance gain Kinetic Energy so they vibrate more

• This means they need more space• So the substance expands

Heat

Important note!

The particles in a substance do not expand themselves!

Heat

Particles are the same size

Contraction

• The opposite happens when most substances are cooled

• The particles vibrate less• They need less room• The substance contracts

Cools

Solids

• The expansion of solids is small but strong!

Like me!

Expansion in solids

This means that we sometimes have to take into account expansion

Expansion in solids

This means that we sometimes have to take into account expansion

Real Life Expansion

• https://www.youtube.com/watch?v=WEfu4H-yyLw

Contraction can also be a problem

Liquids

• Most liquids expand when heated

Gases

• Gases expand a lot when heated!

• http://www.youtube.com/watch?v=A843PL6Yejs&feature=related

• http://www.youtube.com/watch?v=ZgTTUuJZAFs&feature=related

Boyle’s Law

• Review – What was Boyle’s law?

– The volume of a fixed mass of gas is inversely proportional to its pressure, provided its temperature remains constant.

• So what if gasses are heated? What will happen to its volume if pressure remains constant?

Temperature and volume of a gas at constant pressure

• When gas is heated (at constant pressure) the gas expands.

• http://phet.colorado.edu/en/simulation/gas-properties

Investigating Ice (Water)

• Measure (or zero) the mass of a glass beaker.• Place at least 50 g of ice cubes in the beaker.

Measure the mass of the ice cubes.• You will be investigating temperature vs. time

as ice melts.– Measure the initial temperature of the ice (time = 0 s)– Using the hot plate, heat the beaker. Measure and

record the temperature every 30 seconds until all the water has evaporated.

• Create a temperature vs. time graph.

Thermal Capacity

• Thermal Capacity: Amount of heat required to change a substance’s temperature by a given amount.– The higher the thermal capacity, the more heat an

object must absorb to increase its temperature.– Dependent on what the material is made of– Objects such as wood, glass, and plastic have

higher thermal capacities compared to metals such as iron and aluminum.

Specific Heat Capacity

• Specific Heat Capacity : the energy required to raise the temperature of 1kg of substance by 1oC.

• Different substances have different specific heat capacities.

Specific Heat Capacity

Energy = mass x specific heat capacity x change in temperature

Q = mcΔT• Where – Q = energy in J– M = mass in kg– C = specific heat capacity in J /kgoC– ΔT = Tfinal – Tinitial (both in oC)

Examples

• 1. Water has a specific heat capacity of 4200 J/kgoC while sand has a specific heat capacity of 1381 J/kgoC. What does this mean?

• 2. A hot water tank contains 200kg of water at 20oC. How much energy must be supplied to heat this water to 70oC? The specific heat capacity of water is 4200 J/kgoC .

Phase Change

http://cnx.org/contents/5f2b5aef-4948-488f-8ff9-839478a6d6cf@8/Phase_Change_and_Latent_Heat

http://cnx.org/contents/5f2b5aef-4948-488f-8ff9-839478a6d6cf@8/Phase_Change_and_Latent_Heat

Melting/Fusion and Boiling/Vaporization

Latent Heat

• Latent Heat of Fusion – the amount of heat needed to change the state of 1kg of substance from solid to liquid (or vice versa)– Lf = 340,000 J/kg (latent heat of fusion of water)

• Latent Heat of Vaporization – the amount of heat needed to change the state of 1kg of substance from liquid to gas (or vice versa)– Lv = 2,300,000 J/kg (latent heat of vaporization of water)

Evaporation vs. Boiling• Evaporation is not boiling. It is the escape of more

energetic molecules from the surface of a liquid.• With boiling, evaporation is very rapid as vapor

bubbles form throughout the liquid, rise to the top, and burst – releasing large amounts of vapor.

Methods of Heat Transfer - 1

• 1. Conduction – heat transfer between solids.– Molecules in a solid are very close to each other.

When one part of a solid object, say a metal spoon, is heated, the other tip of the spoon will be hot after some time.

Conduction• Types of Materials:• a) Conductors – materials that allow heat to

transfer rapidly.– Metals are good examples

of conductors.

• b) Insulators – materials that do not rapidly allow heat to transfer.– Wood and plastics are good examples

of insulators.

Methods of Heat Transfer - 2

• 2. Convection – heat transfer between fluids (liquids and gasses)

Methods of Heat Transfer - 3

• 3. Radiation – energy spreading out from a source carried by particles or waves– The hotter the

object, the more infrared radiation it gives out.

Good Absorbers, Good Emitters

• It is the surface that determines whether an object absorbs or reflects infrared radiation.

• A surface that is a good reflector is a poor absorber.

• Matt black surfaces are the best absorbers and best emitters (the worst reflectors).

Home Insulation

• Where does the heat go?

Ways of Retaining Energy in a House

Endothermic and Exothermic

• Follow the instructions at each station carefully and be sure to clean up after yourself! Stay at the station until the buzzer sounds.

• Be sure to record measurements and observations when prompted!

Endothermic and Exothermic

• Read pages 114 - 116, then review each demonstration and decide if the reaction was endothermic or exothermic. Be sure to cite a reason why!

• Define exothermic & endothermic.