Equilibrium - Week 13 - 16 Flashcards
What is the definition of an isolated system?
No energy or matter can go in or out
What is the definition of a closed system?
Energy can go in and out but not matter
What is the definition of an open system?
Energy and matter can come in and out
What is the definition of an adiabatic system?
No heat can go in or out
How do changes arise in closed systems?
Changes arise from loss or gain of heat and work done on or by the system.
Is heat a random or organised movement of particles?
= a random movement of particles
Is work done a random or organised movement of particles?
= an organised movement of particles
What are state functions?
Variables of the system with values independent of how they were produced
e.g. pressure, volume, temperature
Variables can be intensive or extensive
What is an extensive variable?
Value dependent of how much of the system there is (size of system)
What is an intensive variable?
Value is independent of how much of the system there is. (size of system)
What are some examples of extensive variables?
e.g. energy, volume, area, mass, heat capacity
What are some examples of intensive variables?
e.g. thermal conductivity, density, temperature, concentration, pressure, specific heat capacity, surface tension
What equation are changes in state functions designated?
ΔX = (Xf - Xi)
If q = heat absorbed by the system and w = work done on the system
ΔU = q+w where U is the internal energy
q and w are not state functions. U is
What is the equation for the 1st Law of thermodynamics (a statement of the Law of Conservation of Energy)
ΔU = q + w where U is the internal energy
What does the law of conservation of energy require - about the change in energy between two defined states ?
The change in energy between two defined states is independent of the route used between A and B.
What is the equation for enthalpy changes at a constant pressure? H ?
H = U + PV
For changes at constant pressure ΔH = q so ΔH values are usually measured rather than ΔU values.
What is a situation where adding or removing energy by heating or cooling does not produce a change in temperature?
= when changes of state occur for a substance
How do you measure heat entering a system?
q = the heat entering the system (therefore ΔH)
q is equal in magnitude but opposite sign to the heat entering the surroundings
Heat entering the apparatus (calorimeter) = Q
q = -Q
Why do different substances produce different temperature changes for the same value of Q?
Q produces a temperature change which depends on the magnitude and sign of Q, the mass of substance affected and nature of substance.
Therefore different substances may produce different temp changes for the same Q value.
What is the equation that describes the relationship change between Loss of heat (Q), and the temperature change produced by the substance?
Q=mcΔT
What do each of the symbols represent in the equation Q=mcΔT ?
m = mass affected
c = specific heat capacity of the substance
ΔT = temperature change
=> where m and c are positive quantities
For an exothermic change what (positive or negative) are Q and ΔH?
For an exothermic change:
Q = positive
ΔH = negative
What happens to ΔH (positive or negative) in an endothermic change?
Endothermic change = ΔH is positive
What are the units for enthalpy change of a reaction?
kJ mol^-1
What are the standard conditions and standard states for enthalpy changes?
Standard conditions:
- 298K
- 100 kPa (1 atm)
- 1 mol dm^-3
What does ΔH° mean?
ΔH° = standard enthalpy change
What is the standard enthalpy change of reaction, ΔrH°?
The standard enthalpy change of a reaction is the enthalpy change which occurs when equation quantities of materials react under standard conditions, and with everything in its standard state.
What is the equation for Standard enthalpy change of formation, ΔH°f ?
ΔrH° = ΔfH° (prod) - ΔfH° (react)
ΔrH° = products - reactants
What is the ΔH°f of any element?
ΔH°f of any element = 0
What is the equation for enthalpy change of combustion ΔcH° ?
ΔrH° = ΔcH° (react) - ΔcH° (prod)
ΔrH°= reactants - products
What is the equation for bond enthalpy?
(of all gaseous molecules)
ΔrH° = BE (react) - BE (prod)
ΔrH° = reactants - products
What are the only energy changes possible in an isolated system?
Changes where energy becomes more spread out or disorganised
What is entropy (S) ?
Entropy measures how heat spreads out - the ‘disorder’
What is the Gibbs Free Energy equation?
ΔG = ΔH - ΔTS
If ΔG is negative what is TΔS?
TΔS will be positive
-> and the process is likely to occur
If ΔG is positive what is TΔS?
TΔS is negative
-> the process is unlikely to occur