First Law

Question 1

What is Boyle’s law?

Answer 1

pV=constant (where n and T are constant)

Question 2

What is the gas pressure law?

Answer 2

p/T=constant (n and V are constant)

Question 3

What is R in SI units?

Answer 3

8.314 JK^-1mol^-1

Question 4

What is R in non-SI units?

Answer 4

0.08206 dm³atmK^-1mol^-1

Question 5

What is SATP?

Answer 5

Standard ambient temperature and pressure, T=298K, p=1.00x10⁵Pa

Question 6

What is STP?

Answer 6

Standard temperature and pressure, T=0.00ºC, p=1.00atm

Question 7

What is Dalton’s law?

Answer 7

Total pressure=sum of partial pressures

Question 8

Define partial pressure

Answer 8

The pressure a gas would exert if it occupied the container on its own

Question 9

What is the equation for molecular speed?

Answer 9

c=(3RT/m)^1/2

Where m is the molecular mass in kg

Question 10

Whos experiment confirmed the distribution of molecular speeds? Briefly describe the experiment

Answer 10

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

Question 11

How is the rate of effusion related to the molar mass of a gas molecule?

Answer 11

Rate of effusion (=k) (1/M)^½

Question 12

What is the collision frequency?

Answer 12

The average rate of collisions

Question 13

What is the time of flight?

Answer 13

The average time between collisions

Question 14

What is the mean free path?

Answer 14

The average distance travelled between collisions

Question 15

What is the equation for the collisonal cross section of a molecule?

Answer 15

σ=πd²

Where d is the diameter of the molecule (2 same sized atoms can collide in this area)

Question 16

What is the equation of the mean free path?

Answer 16

λ=RT/N_aσp

Where σ is the collision cross section and equals πd²

Question 17

What is the Van der Waals eqaution of state?

Answer 17

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.

Question 18

What is the critical temperature of gases?

Answer 18

The temperature where a gas can be liquified by compression

Question 19

What is a supercritical fluid?

Answer 19

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.

Question 20

What is the vapour pressure of a liquid?

Answer 20

The pressure of the vapour in equlibrium with the liquid at a certain temperature

Question 21

How are vapour pressure and temperature related?

Answer 21

Increase in temperature causes an increase in vapour pressure

Question 22

How is vapour pressure measured?

Answer 22

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

Question 23

On a phase diagram, what is the point where all 3 phases meet called?

Answer 23

The triple point

Question 24

On a phase diagram, what is the end of the gas-liquid line called?

Answer 24

Critical point, where supercritial fluid forms

Question 25

How are K_c and K_p related?

Answer 25

K_p=K_c(RT)^Δn

Question 26

What is K^⦵ and what are its units?

Answer 26

The standard equlibrium constant defined by activities (a), as activities are dimensionless K^⦵ has no units

Question 27

When is K^⦵ numerically equivalent to K_p?

Answer 27

When pressure is measured in bar

Question 28

What is the 0th law of thermodynamics?

Answer 28

If 2 systems are in thermal equlibrium with a 3rd, they are all in thermal equlibrium

Question 29

What is the first law of thermodynamics?

Answer 29

The total internal energy of an isolated system is constant, energy can be transformed from different types but cannot be created or destroyed

Question 30

What is an open system?

Answer 30

Where heat and matter can be exchanged with the surroundings?

Question 31

What is a closed system?

Answer 31

Where heat can be exchanged with the surrounding but not matter

Question 32

What is an isolated system?

Answer 32

Where no heat or matter can be exchanged with the surroundings

Question 33

What is a dithermal wall?

Answer 33

A wall which exchanges heat with its surroundings

Question 34

What is an adiabatic wall?

Answer 34

A wall which doesn’t exchange heat with surroundings

Question 35

What is isothermal change?

Answer 35

Where the system stays the same temperature as the surroundings

Question 36

What is adiabatic change?

Answer 36

Where there is no heat exchange between a system and surroundings

Question 37

Why are exothermic heat changes negative?

Answer 37

Because heat is lost from the system into the surroundings

Question 38

Why is work posistive in H_2(g)+½O_2(g)→H₂O_(l)

Answer 38

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)

Question 39

What 2 equations is work equal to?

Answer 39

-p_exΔV and -ΔnRT

Question 40

What is internal energy?

Answer 40

A measure of all the energy reserves of a system

Question 41

What is ΔU equal to?

Answer 41

q+w and ΔH-ΔnRT(at constant pressure)

Question 42

What is an extensive property? Give an example

Answer 42

A property that depends on the size (extent) of the sample such as U

Question 43

What is an intensive property? Give an example

Answer 43

A property that is independant of size, such as U_m, molar internal energy

Question 44

What is the difference between bond dissociation energy and average bond energy?

Answer 44

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

Question 45

What is the formula for ΔH?

Answer 45

ΔH=ΔU+ΔnRT

Question 46

How is ΔU measured accurately and why can this be done?

Answer 46

Using a bomb calorimeter, as the volume is constant no work can be done so only heat energy is output which is measured

Question 47

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?

Answer 47

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.

Question 48

What is an endothermic compound?

Answer 48

A compound with has an endothermic enthalpy of formation

Question 49

What is Hess’s law?

Answer 49

The standard enthalpy change for a reaction is the sum of the standard enthalpy changes for the reactions into which it can be divided

Question 50

Write Hess’s law out into an equation

Answer 50

Δ_rH=ΣvΔ_fH^⦵_(products)-ΣvΔ_fH^⦵_(reactants)

Where v is the weighting factor (from the stoichiometry)

Question 51

What is an explosion?

Answer 51

A rapid and extreme increase in volume accompanied by energy release. Usually characterised by temperature increase and generation of gases.

Question 52

What 2 molecules are key to the energy release in the body? What is the difference between them?

Answer 52

ATP releases energy, ADP is the lower energy version after it has lost a phosphate

Question 53

What is the equation for specific heat capacity?

Answer 53

q/mΔT

Question 54

What are the units for molar heat capacity?

Answer 54

JK^-1mol^-1

Question 55

What are the 2 heat capacities for gases?

Answer 55

Molar heat capacity at constant pressure, C_p, and molar heat capacity at constant volume, C_v

Question 56

Why do more complex gases such as CO₂ have a higher molar heat capacity than the ideal gas?

Answer 56

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.

Question 57

What is Kirchhoff’s law?

Answer 57

Δ_rH_T2=Δ_rH_T1+Δ_rC_pΔT

Where Δ_rC_p=ΣvC_p(products)-ΣvC_p(reactants)

Question 58

What incorrect assumption does Kirchhoff’s law use for simplification?

Answer 58

C_p is assumed not to change as the temperature changes, intergration is required to accurately calculate enthalpy changes.

Question 59

What is the equation relating the gas heat capacities and why do they have that relationship?

Answer 59

C_p=C_v+R (R changes for different gases) This is because C_p is equivalent to ΔH and C_V is equivalent to ΔU

Question 60

Describe the 2 ways that suncream protects skin

Answer 60

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

Question 61

What is threshold wavelength

Answer 61

The maximum wavelength needed for a chemical process, represented as λ₀