Thermochemistry Flashcards
Isolated system
Cannot exchange energy or matter with surroundings
Closed system
cahn exchange energy but not matter
Open system
can exchange heat and energy i.e. pot of boiling water
Delta U = Q + W
delta U: change in internal energy of the system
Q: heat added to the system
W: work done by the system
Isothermal processes
System’s temperature is constant. Q = W
Adiabatic processes
No heat exchanged between system and environment. (delta) U = -W
Isobaric processes
Pressure of system is constant.
Isovolumetric processes (isochoric)
No change in volume. No work is performed in process. (delta U) = Q
Spontaneous process
A process that can occur by itself or without having to be driven by energy from an outside source. (delta) G helps us predict spontaneity
Standard Conditions
25°C (298K), 1 atm, 1M concentrations; used for measuring enthalpy, entropy, and Gibbs free energy
Standard Temperature and Pressure
0°C (273K), 1 atm
Gas-liquid equilibria
molecules near surface of liquid may have enough energy to jump into gas phase.
Condensation
Gas to liquid. Facilitated by lower temperatures or higher pressures
Sublimation
Solid to gas.
Deposition
Gas to solid
Enthalpy
Average KE of particles and amount of substance present.
(H)
(delta) Hrxn = Hproducts - Hreactants
+ enthalpy = endothermic
- enthalpy = exothermic
Heat
Transfer of energy from one substance to another as a result of a difference in temperature. (Q)
Q > 0: endothermic
Q < 0: exothermic
Zeroth Law of Thermochemistry
Objects are only in thermal equilibrium when their temperaturs are equal.
q= mc(delta)T
q: heat absorbed or release (J or cal)
m: mass
c: specific heat (cal/g x K)
cH20 = 1 cal/g x K
heat capacity
mass x specific heat
Heating Curve
q = mL
m = mass
L= Latent heat (cal/g)
Used during phase changes
Standard enthalpy of formation
(delta)Hf°
The enthalpy required to produce one mole of a compound from its elements in their most stable physical states (standard states).
Standard heat of a reaction
(delta)H°rxn
ΣH°f,products - ΣH°f,reactants
Hess’s Law
(delta)H = (delta)H1 + (delta)H2+(delta)H3 + (delta)H4
Bond dissociation energy
Energy needed to break a type of bond between atoms in the gas phase. (endothermic)
KJ/mol of bonds broken
Standard heat of combustion
(delta)H°comb
The enthalpy change associated with the combustion of a fuel.
Second Law of Thermodynamics
Energy spontaneously disperses from being localized to becoming spread out if it is not hindered from doing so.
Entropy
The measure of spontaneous dispersal of energy at a specific temperature. How much energy is spread out, or how widely spread out energy becomes, in a process.
(Delta)S = Qrev/T
Qrev = heat that is gained or lost in a reversible process
T = temp in Kelvin
Units: J/(mol x K)
Gibbs free energy
Measure of change in enthalpy and entropy; predicts whether a process is spontaneous or nonspontaneous.
