Lecture 7 Flashcards
First law of thermodynamics
Total energy if system + surroundings always remains constant
Δ E (universe) = Δ E (system) + Δ E (surroundings) = 0
State functions
The value of a state function depends on the state of the system not how we arrived at that state
Name a state function
Internal energy
Δ E of a chemical reaction =
= E products - E reactants
= q + w
Two most important types of chemical work…
- electrical
- Pressure
Electrical work
Moving charged particles
Pressure work
Volume work (PV work)
PV work
Work done when volume of system changes due to presence of external pressure
Enthalpy (H) =
= E + PV
Δ H = Δ E + Δ PV
Delta H ≈ Delta E
If a system remains at constant pressure and it’s volume does not change much
Δ H
The change in heat for a system at constant pressure
Exothermic reaction
- ΔH < 0
- heat is released
Endothermic reaction
- ΔH > 0
- heat is absorbed
Heat of reaction (ΔHrxn)
Enthapy change for chemical reaction (exothermic)
Heat of combustion (ΔHcomb)
Enthalpy change for the chemical reaction when 1 moo of a substance reacts with O2 (exothermic)
Heat of formation (ΔHf)
Enthalpy change for the chemical reaction when 1 mom if a compound is produced from its compone t elements (exothermic)
Heat of fusion (ΔHfus)
Enthalpy change for the melting or freezing of 1 mil if a substance
Melting ΔH > 0
Freezing ΔH < 0
Heat of vaporation (ΔHvap)
Enthalpy change for the vaporization or condensation of 1 mol of substance
Vaporization ΔH > 0
Condensation ΔH < 0
Calorimetry
A apparatus measuring the amount of heat involved in a chemical reaction or other process
Equation : q =
c x m x ΔT
Specific heat capacity
The quantity of heat required to change the temperature of 1 gram of the substance by 1K (kelvin)
Thermochemistry equation
A balanced equation that includes ΔHrxn
ΔH is proportional to…
The amount of substance
Decomposition
AB -> A + B
Formation
A +B -> AB
