Guided Notes: Heat & Temperature

Heat & Temperature Temperature – a measure of the average kinetic energy of each particle within an object. Three temperature scales - Fahrenheit, Celsius, & Kelvin.

Heat (Thermal Energy) – the total energy of the particles that make up an object. Heat transfer – thermal energy moves from an object at a higher temperature to an object at a lower temperature. .

Heat Transfer – occurs by conduction, convection, and radiation. Conductors – transfer heat well.

Specific Heat – the amount of heat necessary to raise a given mass of a substance by a specific unit of temperature. Matter can exist in three states: solid, liquid, or gas. Matter can undergo a change of state when thermal energy is added or removed.

When a substance is changing state, the temperature of the substance remains constant. There are potential energy changes. In general, matter expands when it is heated and contracts when it is cooled.

Change of State – The Physical change of matter from one state (or phase) to another

Melting – The change from a solid to the liquid form of matter. The Melting Point – The temperature at which a substances melts.

Freezing – the change from a liquid to a solid. Freezing Point – The temperature at which a substance freezes.

Vaporization – The change from a liquid to a gas. Evaporation – Vaporization that occurs at the surface of a liquid.

Boiling – Vaporization that occurs below the surface of a liquid. Boiling Point – The temperature at which a liquid substance boils.

Condensation The change from a gas to the liquid.

Why is it true that a cup of boiling water contains less heat than a large iceberg? An Iceberg is Huge compared to a cup of boiling water. Icebergs have greater stored energy.

Thermal Energy Which beaker of water has more thermal energy? Beaker B: - same temperature, more mass Beaker B Beaker A

Heat Transfer Why does a beaker of water at 80º feel hot while a beaker of water at 10º feel cold? Heat flows from A to your hand = hot Heat flows from your hand to B = cold Beaker B has more thermal energy 10ºC 80ºC

Heat Transfer Heat is always transferred from hot to cold. Insulation slows the transfer of heat due to air pockets. Conductors easily allow the transfer of heat, like metals. Heat is transferred by conduction, convection, and radiation.

Conduction Heat is transferred due to objects touching each other or through collusions. Occurs best in solids. Heat continues to be transferred until both objects reach the same temperature called thermal equilibrium.

Convection Transfer of heat through a liquid or gas through moving currents called convection currents. The cause of wind and weather.

Radiation Transfer of heat through electromagnetic radiation (light from stars or light bulbs) Transferred in all directions No contact required Dark or dull objects absorb more than light or shiny objects do.

Heat Transfer Specific Heat (Cp) - amount of energy required to raise the temperature of 1 kg of a material by 1 degree Kelvin. Units: J/(kg K) or J/(g°C)

Heat Transfer Which sample will take longer to heat to 100°C? Aluminum – It has a higher specific heat Aluminum –will also take longer to cool down.

Specific Heat Heat (Q) depends on 3 things:

q = m(∆T)Cp Specific Heat amount of heat transferred = mass x change in temperature x specific heat q = m(∆T)Cp

Can you picture a piece of aluminum foil that is taken out of an oven. Example: Aluminum has a specific heat of 0.902 J/g x oC.   How much heat is lost when a piece of aluminum with a mass of 23.984 g cools from a temperature of 415.0 oC to a temperature of 22.0 oC? Step 1:  First read the question and try to understand what they are asking you.  Can you picture a piece of aluminum foil that is taken out of an oven.  Imagine the aluminum losing heat to its surroundings until the temperature goes from 415.0 oC to  22.0 oC.

Step 2:  Write the original formula.

Step 3: List the known and unknown factors Step 3:  List the known and unknown factors.   Looking at the units in the word problem will help you determine which is which. q = ? m = 23.984 g ∆T = (415.0 oC - 22.0 oC) = 393.0 oC     (remember, they asked for the change in temperature) Cp =  0.902 J/g x oC

Step 4.  Substitute your values into the formula q = ? m = 23.984 g DT = (415.0 oC - 22.0 oC) = 393.0 oC   Cp =  0.902 J/g x oC