CHAPTER 2  Heat  Temperature and Conversions  Specific Heat

What is Energy?  The ability to move or change matter. (Units: Joules)  All physical and chemical changes involve energy!

Examples of Energy  Kinetic – energy of motion  KE = ½ mv 2  Potential – stored energy/energy of position  Light  Sound  Electricity  Heat (Thermal)  Chemical

Law of conservation of energy:  Energy cannot be created or destroyed during any chemical or physical change. Energy may be transferred between the system and surroundings Energy may change forms.

Energy and mass are related  Einstein derived an equation to show this relationship in  Nuclear reactions can create energy from mass.

Energy is transferred during physical and chemical changes:  Endothermic – energy is absorbed by the system +  Exothermic – energy is released into the surroundings -

What is Heat?  The transfer of energy between the particles of two objects due to a temperature difference between the two objects.  Heat always flows from hot to cold.  Measured in a calorimeter.  Units: Joules, Calories, or calories.

TEMPERATURE What is temperature?  Temperature is the measure of the average kinetic energy of all the particles within an object.  Measured with a thermometer.

Heat and temperature  The transfer of heat does not always result in a temperature increase. During phase changes, energy goes directly to changing the phase, not into increasing the kinetic energy of the particles.  EX. The heating curve for water.

The heating curve for water shows that temperature does NOT change during a phase change.

Heating curve points and definitions:  Melting point/ freezing point of water: 0º C  Boiling point of water: 100 º C  Heat of fusion – the amount of energy required to melt a solid  Heat of crystallization – the amount of energy released when a solid forms from a liquid  Heat of vaporization – the amount of energy required to change a liquid into a gas.

Scales to Measure Temperature  Fahrenheit Scale (U.S.A.)  Celsius Scale (everyone else)  Kelvin Scale (scientists)

How do Thermometers Work?  Usually contain alcohol or mercury.  Temperature increase (particles move faster), liquids expand  Temperature decreases (particles move slower), liquids contract

Absolute Zero  The lowest possible temperature  All motion STOPS.  Energy is minimal/absent.  In September 2003, MIT announced a record cold temperature of 450 pK, or 4.5 × K in a Bose-Einstein condensate of sodium atoms. This was performed by Wolfgang Ketterle and colleagues at MIT.September 2003MITWolfgang Ketterle

SPECIFIC HEAT CAPACITY  Transfer of heat affects substances differently.  Measuring heat transferred to and absorbed by a substance under conditions of constant pressure yields specific heat capacity.

SPECIFIC HEAT CAPACITY Specific heat is defined as: The quantity of heat required to raise 1 gram of a substance 1°C or 1 K. Symbol: Cp The p symbolizes that the measurements were taken under constant pressure. Units = Joules/ gram °C or J/gK J/g°C

Sample Cp values  Metals have low specific heat values which allows them to heat up with little added energy.  Iron J/g°C  Copper J/g°C  Platinum J/g°C  Water has a relatively high specific heat J/g °C

Questions:  Which would heat up faster, 5.00 grams of iron or 5.00 grams of water?  Which would cool down faster, 5.00 grams of iron or 5.00 grams of water?  Which is a better thermal conductor?  Which is a better insulator?

MEASURING HEAT and SPECIFIC HEAT Must use a calorimeter. Find the change in temperature:  T = (delta T) change in temperature in °C  T = T final – T initial

SPECIFIC HEAT CALCULATIONS q =m x Cp x  T

Rearrange the formula: m= q/Cp  T Cp = q/ m  T  T = q/ m Cp