Summary Energetics I

Topic 8: Energetics I
1. know that standard conditions are 100 kPa and a specified temperature,
usually 298 K
Standard Conditions
Temperature: 298K
Pressure: 100kPa

Standard conditions are used to show enthalpy changes because they are affected by
temperature and pressure. H means the measurements were taken under standard
conditions.

2. know that the enthalpy change is the heat energy change measured at
constant pressure
Enthalpy change H: the heat change in a reaction at a constant pressure (kJ/mol)

Endothermic: reactions absorb heat energy so H is positive
 indicated by a decrease in temperature
 when bonds are broken
 CaCO3(s)  CaO(s) + CO2(g) rH = +178 kJ/mol
Exothermic: reactions release heat energy so H is negative
 indicated by an increase in temperature
 when bonds are made
 CH4(g) + 2O2(g)  CO2(g) + 2H2O(l) cH = -890kJ/mol



3. be able to construct and interpret enthalpy level diagrams showing an
enthalpy change, including appropriate signs for exothermic and
endothermic reactions
Endothermic Exothermic


Enthalpy
level
diagram




Reaction
profile
diagram