Unit 6 - Thermodynamics

System

the part of the universe on which attention is focused

Surroundings

everything esle and exchange energy with the system

Open system

Exchange mass & energy

closed system

exchange energy

isolated system

exchanges nothing

First law of thermodynamics

Energy is neither created nor destroyed

Exothermic

Heat released to surroundings; negative; increase temp; frees energy when forming bonds

Endothermic

Heat absorbed from surroundings; positive; decrease temp; takes energy to break bonds

Exothermic energy phase change

Freezing, condensation, depositon ( Gas to solid)

Endothermic phase change

Melting, vaporization, sublimation(solid to gas)

Determine molar heat

Calculating heat q= mass x specific heat x change in temperature

Temperature does not rise during phase change because

The heat goes into pulling the molecules further apart

Calculating bond enthalpy

Breaking - making

Calculate the DeltaH(rxn)

Products - reactants

When you reverse an equation

Flip the sign of Delta h

Calculation of Delta H using Hess's law

q=mΔHfus​

heat of fushion