Physical Flashcards
What is the zeroth law of thermodynamics?
If system A is in thermal equilibrium with B, and B is in thermal equilibrium with C, then C is also in equilibrium with A
What is the first law of thermodynamics?
Energy cannot be created or destroyed but it can be converted into another form
ΔU = q + w
ΔU = internal energy q = heat w = work
When work is done on a system, is w positive or negative?
Positive
When heat is gained by a system, is q positive or negative?
Positive
What are adiabatic systems?
Thermally insulated, isolated systems
Heat is not involved
What is an isothermal system?
Closed, not thermally isolated systems
What is an isovolumetric process?
Volume is constant, pressure and temperature can change
Heat is allowed to enter
What is an isobaric process?
Pressure is constant, volume and temperature can change
Heat is allowed to escape
What is an isothermal process?
Temperature is constant, pressure and volume can change
Adiabatic process
Pressure, volume and temperature can all change
Heat isn’t allowed to escape
What is the second law of thermodynamics?
ΔS univ > 0
Heat cannot spontaneously flow from a colder location to a hotter location
The total entropy of the universe always increases
What is the third law of thermodynamics?
S T=0 >= 0
As a system approaches absolute zero all thermal processes cease and entropy approaches a minimum
What is a perfect crystal?
- when entropy = 0
- atoms or ions are arranged in a regular, uniform way
What is enthalpy and how can it be calculated from internal energy?
A measure of the total energy of a thermodynamic system
H = U + PV
U= internal energy
What are the two types of calorimeter?
- constant volume
- constant pressure
Define specific heat capacity
The energy required to raise the temperature of 1g of substance by 1°C
State Hess’s Law
The enthalpy change for a reaction is independent of the route taken
Define electron affinity
The energy released when an electron is added to a gaseous atom
X(g) + e- -> X^- (g)
Define energy of atomisation
The energy needed to transform an element in its standard state into 1 mole of gaseous atoms
How does heat differ from temperature?
Heat is a measure of thermal energy flow
Temperature is the average thermal energy per atom
What is thermal energy?
The kinetic and potential energy associated with the movement of individual molecules and atoms
What is bond dissociation enthalpy and how does it differ from bind energy?
Bind dissociation enthalpy is the energy required to break 1 mole of specific binds at RTP
BDE is specific for a particular bind in a particular molecule
Bond energy is the average value to break a bond across various molecules
What is a spontaneous reaction?
A reaction that does occur under specific conditions
What is a non-spontaneous reaction?
A reaction that does not occur under specific conditions
Define standard entropy of reaction
The entropy change for a reaction carried out at 1 atm and 298K
Units of J K-1 mol-1
Define Gibbs free energy
The energy available to do work at constant pressure
Which gas law relates pressure and volume?
Give the equation for it
Boyle’s law
P1 V1 = P2 V2
What does Gay-Lussac’s law involve? Give the equation
Temperature and pressure
P1 / T1 = P2 / T2
What does Charles’s law relate? Give the equation
Temperature and volume
V1 / T1 = V2 / T2
What relates volume and amount in gases? Give the equation
Avogadro’s law
V1 / n1 = V2 / n2
Explain why the behaviour of a real gas might be different to predictions made using the ideal gas law
In an ideal gas, molecules do not attract or repeal one another
The volume is negligible compared with the volume of the container
Real gases act like ideal gases at 0°C and 100 kPa
How would you calculate the density of a gas?
d = Mr P / RT
What is the equation for calculating concentrations of gases?
C = P /RT
What is Dalton’s law of partial pressures?
The total pressure of a mixture of gases is just the sum of the pressures that each gas would exert if it were present alone
What does Boyle’s law state?
For a fixed mass of gas at constant temperature, the volume is inversely proportional to the pressure
What does Charles’s law state?
For a fixed mass of gas at constant pressure, the volume is directly proportional to the temperature
What does Gay-Lussac’s law state?
The pressure of a fixed amount of gas at a constant volume is proportional to temperature
What does Avogadro’s law state?
The volume of a gas maintained at a constant pressure and temperature is proportional to the amount of gas
What is the equation for calculating the partial pressure of a gas?
P = mole fraction x total pressure
What is the equation for calculating mole fraction of a gas?
X = no. of moles of gas A / total number of moles of gas
What is Le Cháteliers principal?
A system at equilibrium will oppose any change made to the system
Equation that links equilibrium constant with Gibbs free energy
ΔG° = -RT ln(k)
What is a bronsted acid?
Proton donor
What is a bronsted base?
A proton acceptor
What is the Henderson-Hasselbalch equation?
pH = pKa + log10([A-] / [HA])
Explain what is meant by rate law and reaction order
Rate law expresses the relationship of the rate of a reaction to the rate constant and the concentrations of the reactants raised to some power
Reaction order is the sum of the individual orders in a reaction (the overall order)
What is the intergrated rate equation for a zeroth order reaction?
[A] = [A]0 - nkt
What is the equation for calculating the half-life of a zeroth order reaction?
t 1/2 = [A]0 / 2nk
What is the integrated rate equation for a first order reaction?
[A] = [A]0 e^(-nkt)
What is the equation for calculating the half-life of a first order reaction?
t 1/2 = ln(2) / nk
What is the integrated rate equation for a second order reaction?
1/[A] = 1/[A]0 + nkt
What is the equation for calculating the half-life of a second order reaction?
t 1/2 = 1/ nk [A]0
What is half-life?
The time taken for the concentration of a reactant to drop to half of its initial value
What is the equation relating Kp to Kc?
Kp = Kc (RT)^Δn
What is the equation relating Kp to Kc?
Kp = Kc (RT)^Δn
