Heating and Cooling Curves

Heat vs Temperature Heat is the total molecular energy (kinetic and potential); measured in Joules (J) dependent on # particles present Temperature is a measure of kinetic energy of molecules; measured in Celsius NOT dependent on the particles If heat is added, temperature will increase

Heat is used in 2 ways Change temperature heat added: KE increase; molecules speed up heat removed: KE decrease; molecules slow Change state/phase heat added: PE increase; IMFs weaken heat removed: PE decrease; IMFs strengthen

IMFs Intermolecular Force = “The Force” that holds solids and liquids together.

Phase Changes Gas Liquid Solid

Melting and Freezing Points Freezing Point = the temperature when a liquid turns to a solid Melting Point = the temperature when a solid turns to liquid REVERSIBLE processes...therefore mp = fp For water : 0 degrees Celsius

Heating Curve Heat Added ----> Temperature (o C) 1 2 3 4 5

Segment 1 Solid No phase change; solid increases in temp Molecules are moving faster Potential Energy: No Change Kinetic Energy: Increase

Segment 2 Solid and Liquid Melting; no temp change IMFs are being broken Potential Energy: Increase Kinetic Energy: No Change

Segment 3 Liquid No phase change; liquid increases in temp Molecules are moving faster Potential Energy: No Change Kinetic Energy: Increase

Segment 4 Liquid and Gas Boiling; no temp change IMFs are being broken Potential Energy: Increase Kinetic Energy: No Change

Segment 5 Gas No phase change; gas increases in temp Molecules are moving faster Potential Energy: No Change Kinetic Energy: Increase

Cooling Curve 1 2 Temperature (o C) 3 4 5 Heat Removed --->

Segment 1 Gas No phase change; gas decreases in temp Molecules are moving slower Potential Energy: no change Kinetic Energy: decreases

Segment 2 Gas and Liquid Condensing, no temperature change IMFs are being restored Potential Energy: Decreases Kinetic Energy: No Change

Segment 3 Liquid No phase change; liquid decreases in temp Molecules are moving slower Potential Energy: no change Kinetic Energy: decreases

Segment 4 Liquid and Solid Freezing; no temperature change IMFs are being restored Potential Energy: Decreases Kinetic Energy: No Change

Segment 5 Solid No phase change; solid decreases in temp Molecules are moving slower Potential Energy: No change Kinetic Energy: Decreases

Vaporization and Boiling Point Vaporization: liquid → gas Evaporation occurs without heat Boiling occurs when the vapor pressure and the atmospheric pressure are equal. Boiling Point the temperature at which a liquid boils at standard pressure (1 atm)

Calculating Heat for Temperature Change Q = mC∆T Q = Heat Lost (-) or Heat Gained (+) in Joules (J) m = mass (g) C = Specific Heat Capacity (J/goC) ∆T = Change in Temperature (oC) = Tfinal - Tinitial

Calculating Heat for Phase Change Q melt/freeze = mLfusion Qboil/condense = mLvaporization Q = Heat Lost (-) or Heat Gained (+) in Joules (J) m = mass (g) L = Latent Heat (J/g)