Heat Capacity v Specific Heat Capacity

So how fast does an object heat up? Heat Capacity Specific Heat Capacity Definition - amount of thermal energy that warms or cools the object by 1 degree Celsius - amount of thermal energy that warms or cools one gram of a material by one degree Celsius Describes - a particular object- material the object is made of Depends On - mass of the object and material the object is made of - material the object is made of

Changing of States What does “changing of states” mean? When something goes from either solid/liquid/gas to another form solid/liquid/gas Water is a great example… – It can melt (solid ice can melt to liquid water) – It can freeze (liquid water to solid ice) – It can become a gas (from liquid water to water vapour - gas - when it is boiled)

Changing of States What does “changing of states” mean? When something goes from either solid/liquid/gas to another form solid/liquid/gas Water is a great example… – It can melt (solid ice can melt to liquid water) – It can freeze (liquid water to solid ice) – It can become a gas (from liquid water to water vapour - gas - when it is boiled) There is a change of state where it breaks the natural progression … hops from solid directly to gas This is known as sublimation

Change of State Any pure substance can exist in all 3 states – Often easier said than done but it is doable Time for a review! Find a partner Write “Thermal Energy” & “Temperature” & “Energy” on a piece of paper and … … explain to me the difference between them!

Thermal vs. Temperature Review Simply put, heat is the flow of thermal energy. Temperature represents average thermal energy. Heat goes from objects with high temperature to low temperature, not high thermal energy to low thermal energy. (Like diffusion) For example, a massive glacier will have more total thermal energy than a small hot nail (simply because it has more molecules); however, its temperature is lower because it has less average thermal energy. Therefore, energy will be transferred from the nail to the glacier... Thermal energy is the total internal energy of the system. i.e. how fast the molecules are vibrating

Evaporation When you sweat you tend to cool off … why? Enter Particle Model Imagine a liquid (we will use water) in a jar … Top = moving fast (enough to escape) Middle/Lower = slower moving particle stay in liquid state Slower moving = lower temperature That means what is left is cooler … WHAT?!

Evaporation When you sweat you tend to cool off … why? Enter Particle Model Imagine a liquid (we will use water) in a jar … Top = moving fast (enough to escape) Middle/Lower = slower moving particle stay in liquid state Slower moving = lower temperature That means what is left is cooler … This is known as… Evaporative Cooling

Examples of Evaporative Cooling Joggers feel cold as their clothes dry out after a rain storm Home owners spray water on the roof to cool house in hot some day First aid worker puts a cool cloth on your head

Examples of Evaporative Cooling During a change of state (phase) the total energy of a substance … – Increases or decreases Why? – They don’t change speed they change state

Transferring Energy You hold your hand beside a light bulb … your hand warms up – why? The light bulb is an energy source – An object or material that can transfer its energy to other objects

Transferring Energy - Radiation The sun shines billions of kms away but we feel it Energy is transferred even though no material has travelled from the sun to us, solar cells, etc… What is this transfer called? Radiation – Transfer of energy without any movement of matter Energy transferred this way is called Radiant Energy or Electromagnetic Radiation (EMR)

Transferring Energy - Radiation EMRs can travel through all kinds of material and they have some unique characteristics … – Behave like a wave – Absorbed & Reflected by objects – Travel really fast (300,000 km/s) Colours play a role in absorption / reflection of heat radiation (heat waves) – Dark colour absorb – White colours reflect

Transferring Energy - Conduction Conduction is the transfer of energy when particles collide – Simply put … direct contact To do this we need two different types of materials – Conductors … most metals as they carry a current or heat well throughout their entire material – Insulator … these are poor conductors such as wood or glass so they are good at trapping heat/cold and preventing it from escaping

Transferring Energy - Convection Convection is the movement of particles (typically in fluids) carrying its thermal energy with it as it moves Can create a current … how? – Heat rises, cools off, drops back down, heats back up and rises again, repeat … Warmer solutions/particles are less dense Cooler solutions/particles are more dense Dense = amount of matter/particles in a solution

Transferring Energy - Convection

Transferring Energy Systems

Transferring Energy - System Energy Source – The part of the system that supplies the energy to the system Direction of Energy Transfer – Always transferred away from the concentrated source Energy Transformation – Not created or destroyed but transferred from place to place

Transferring Energy - System Waste Energy – Little amount of thermal energy lost to surroundings not involved directly in the transfer Control System – What controls the energy transfer

Thermal Energy Think back … what is thermal energy? – Correct – Energy generated by the movement or vibration of particles That being said there must be a whole bunch of different sources! – Oh yes … yes there are!

Transferring Energy - System