What is Boyle’s law?
pV=constant (where n and T are constant)
What is the gas pressure law?
p/T=constant (n and V are constant)
What is R in SI units?
8.314 JK-1mol-1
What is R in non-SI units?
0.08206 dm3atmK-1mol-1
What is SATP?
Standard ambient temperature and pressure, T=298K, p=1.00x105Pa
What is STP?
Standard temperature and pressure, T=0.00ºC, p=1.00atm
What is Dalton’s law?
Total pressure=sum of partial pressures
Define partial pressure
The pressure a gas would exert if it occupied the container on its own
What is the equation for molecular speed?
c=(3RT/m)1/2
Where m is the molecular mass in kg
Whos experiment confirmed the distribution of molecular speeds? Briefly describe the experiment
The Zartmann expermient used tin molecules vapourised and formed into a beam passing through a slit of a rotating disk which then mark another rotating disk on the same axel. The vapour was pulled through using a vacuum
How is the rate of effusion related to the molar mass of a gas molecule?
Rate of effusion (=k) (1/M)½
What is the collision frequency?
The average rate of collisions
What is the time of flight?
The average time between collisions
What is the mean free path?
The average distance travelled between collisions
What is the equation for the collisonal cross section of a molecule?
σ=πd2
Where d is the diameter of the molecule (2 same sized atoms can collide in this area)
What is the equation of the mean free path?
λ=RT/Naσp
Where σ is the collision cross section and equals πd2
What is the Van der Waals eqaution of state?
Pressure is corrected to account for particles being attracted to each other before colliding with a wall reducing the pressure. Volume is corrected by subtracting the volume occupied by gas molecules.
What is the critical temperature of gases?
The temperature where a gas can be liquified by compression
What is a supercritical fluid?
A substance above its critical temperature and pressure where it no longer acts as a equlibrium of gas and liquid, instead it acts as a mixture of the two.
What is the vapour pressure of a liquid?
The pressure of the vapour in equlibrium with the liquid at a certain temperature
How are vapour pressure and temperature related?
Increase in temperature causes an increase in vapour pressure
How is vapour pressure measured?
Using a mercury manometer, a tube of mercury(resting in mercury) with a pocket of vacuum at the top of the tube. The vapour is injected into the tube and the change in height of the volume the mercury fills is the vapour pressure in mmHg
On a phase diagram, what is the point where all 3 phases meet called?
The triple point
On a phase diagram, what is the end of the gas-liquid line called?
Critical point, where supercritial fluid forms
How are Kc and Kp related?
Kp=Kc(RT)Δn
What is K⦵ and what are its units?
The standard equlibrium constant defined by activities (a), as activities are dimensionless K⦵ has no units
When is K⦵ numerically equivalent to Kp?
When pressure is measured in bar
What is the 0th law of thermodynamics?
If 2 systems are in thermal equlibrium with a 3rd, they are all in thermal equlibrium
What is the first law of thermodynamics?
The total internal energy of an isolated system is constant, energy can be transformed from different types but cannot be created or destroyed
What is an open system?
Where heat and matter can be exchanged with the surroundings?
What is a closed system?
Where heat can be exchanged with the surrounding but not matter
What is an isolated system?
Where no heat or matter can be exchanged with the surroundings
What is a dithermal wall?
A wall which exchanges heat with its surroundings
What is an adiabatic wall?
A wall which doesn’t exchange heat with surroundings
What is isothermal change?
Where the system stays the same temperature as the surroundings
What is adiabatic change?
Where there is no heat exchange between a system and surroundings
Why are exothermic heat changes negative?
Because heat is lost from the system into the surroundings
Why is work posistive in H2(g)+½O2(g)→H2O(l)
Because there is a decrease in moles of gas so the surroundings do work on the system (this can be explained by considering a gas syringe being pushed by a reaction producing gas, the system does work on the syringe)
What 2 equations is work equal to?
-pexΔV and -ΔnRT
What is internal energy?
A measure of all the energy reserves of a system
What is ΔU equal to?
q+w and ΔH-ΔnRT(at constant pressure)
What is an extensive property? Give an example
A property that depends on the size (extent) of the sample such as U
What is an intensive property? Give an example
A property that is independant of size, such as Um, molar internal energy
What is the difference between bond dissociation energy and average bond energy?
Bond dissociation energy refers to a specific internal energy change when a bond in a compound dissociates, average bond energy refers to the type of bond across a range of related compounds
What is the formula for ΔH?
ΔH=ΔU+ΔnRT
How is ΔU measured accurately and why can this be done?
Using a bomb calorimeter, as the volume is constant no work can be done so only heat energy is output which is measured
When a combustion reaction is taking place why must the temperature of the reaction be carefully considered and what effect will this have on ΔH of a reaction?
If the temperature is above 373K then any water produced will be gaseous which will reduce the ΔH of an exothermic reaction. If the temperature is high enough for a reactant to evapourate then the ΔH will become more exothermic.
What is an endothermic compound?
A compound with has an endothermic enthalpy of formation
What is Hess’s law?
The standard enthalpy change for a reaction is the sum of the standard enthalpy changes for the reactions into which it can be divided
Write Hess’s law out into an equation
ΔrH=ΣvΔfH⦵(products)-ΣvΔfH⦵(reactants)
Where v is the weighting factor (from the stoichiometry)
What is an explosion?
A rapid and extreme increase in volume accompanied by energy release. Usually characterised by temperature increase and generation of gases.
What 2 molecules are key to the energy release in the body? What is the difference between them?
ATP releases energy, ADP is the lower energy version after it has lost a phosphate
What is the equation for specific heat capacity?
q/mΔT
What are the units for molar heat capacity?
JK-1mol-1
What are the 2 heat capacities for gases?
Molar heat capacity at constant pressure, Cp, and molar heat capacity at constant volume, Cv
Why do more complex gases such as CO2 have a higher molar heat capacity than the ideal gas?
An ideal gas can only vibrate faster however more complex gases have bonds that can vibrate and stretch so more energy is required to make the molecules themselves vibrate.
What is Kirchhoff’s law?
ΔrHT2=ΔrHT1+ΔrCpΔT
Where ΔrCp=ΣvCp(products)-ΣvCp(reactants)
What incorrect assumption does Kirchhoff’s law use for simplification?
Cp is assumed not to change as the temperature changes, intergration is required to accurately calculate enthalpy changes.
What is the equation relating the gas heat capacities and why do they have that relationship?
Cp=Cv+R (R changes for different gases) This is because Cp is equivalent to ΔH and CV is equivalent to ΔU
Describe the 2 ways that suncream protects skin
They ‘block’ sunlight with a reflective layer (white TiO2/ZnO mineral based)
They filter out harmful high energy photons, UV-A (315 to 400nm) and UV-B (280 to 315nm) using molecules such as octyl salicylate
What is threshold wavelength
The maximum wavelength needed for a chemical process, represented as λ0