physical chemistry

what elements must you mention with ionisation energy trends?

nuclear charge, atomic radius, electron shielding

what model of the atom do trends in ionisation energy support?

the bohr model supports these trends

giant covalent lattice propertiers explained

high melting and boiling points and insoluble due to strong covalent bonds, can only conduct if there are delocalised electrons like graphene and graphite

trend in reacivity down group 2

more reactive as you go down due to a decrease in ionisation energy (more electron shielding, increased atomic radius)

trend in alkalinity of group 2 hydroxide solutions

alkalinity increases as solubility increases down the group

group 2 compound uses

Ca(OH)2 to neutralise soils in agriculture, Mg(OH)2 and CaCO3 as antacids in treating indigestion

halogen boiling point trend

boiling point increased and reactivity decreases down the group due to increased electrons so stronger london forces

halogen reactivity in terms of first ionisation

harder to form -1 ions down the group due to lower nuclear attraction, higher atomic radius, and more elctron shielding so it’s harder to gain another electron.

what is a disproportionation reaction?

the same element is both oxidised and reduced in the same reaction

benefits and risks of chlorine in water treatment

kills harmful bacteria, toxic gas, chlorinated hydrocarbons are carcinogenic

silver nitrate and Cl- ions appearance

white precipitate

silver chloride and weak ammonia

dissolves precipitate. clear solution

silver nitrate and Br- ions reaction appearance

cream precipitate

silver nitrate and I- ions appearance

yellow precipitate

silver bromide reaction with ammonia

no reaction with weak, dissolves to clear solution with strong

silver iodide with ammonia

no reaction no matter strong or weak

disproportionation examples

Cl2 in water makes HClO +1 and HCl -1, Cl2 and cold dilute NaOH NaCl -1 and NaClO +1

ammonia NH3 test

mix with warm dilute NaOH(aq) if positive damp red litmus paper turns blue

is bond breaking exo or endothermic

bond breaking is endothermic

is bond making exo or endothermic

bond making is exothermic

label the diagram

A reactants

B products

C Ea activation energy

D ΔH enthalpy change

E reaction progress

F enthalpy kJ/mol

Exothermic

enthalpy change ΔH

the change in heat energy of a substance expressed at a constant pressure

how to calculate enthalpy change

products - reactants

standard enthalpy of combustion ΔHc

the enthalpy change when one mole of a compound is burned completely in oxygenated standard conditions

what is ΔHθ

the change in heat energy under standard conditions 100kPa 298K

amount of heat gained or lost by a sample

q=mc∆T

q is heat lost/gained (J)

m is the mass of water/solution (g)

c specific heat capacity of water (J/g/K)

∆T change in temp (K)

enthalpy change of reaction ΔH^ºr

the enthalpy change of a reaction in moles with reactant and products in standard states and conditions

average bond enthalpy

the average enthalpy change that takes place when breaking by homolytic fission one mole of a given type of bond in the molecules of a gaseous species

enthalpy change of formationΔH^ºf

the enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions

standard enthaloy of formation of elements in theur natural states

0kJ/mol

standard enthalpy change of neutralisation ΔH^ºc

the enthalpy change that accompanies the reaction of an acid by a bse to from one mole of H20(l) with all reactants and products in their standard states under standard conditions

standard conditions

298k/25c 1atm pressure/101kPa 1moldm³

Hess’s law

if a reaction can take place by 2 routes, the total enthalpy change is the same for each route, providing that the start and end conditions are the same

endothermic reaction enthalpy change

positive

exothermic reaction enthalpy change

negative

what is the collision theory

for a chemical reaciton to take place the particcles need to collide with each other in the correct orientastion and enough energy

ineffective collision

particles collide in the wrong orientation or when they don’t haver enough energy and bounce off each other without causing a chemical reaction

what is collision frequency

number of collisions per unit time

effect of concentration on reaction rate

increase in collision frequency and rate of reaction

effect of pressure on reactions

increase

reaction rate formula

change in amount of reactants or products (mol dm^-3) / time (s)

role of a catalyst

a substance that increases the rate of reaction by providing the particles with an alternative mechanism with a lower activation energy

types of catalyst

homogeneous and heterogeneous

homogeneous catalyst

the catalyst is in the same place as the reactants (e.g everything is in solution)

heterogeneous catalyst

the catalyst is in a different phase to the reactants (e.g reactants are gases catalyst is a solid)

catalyst benefits

lower temparature and pressure can be used

reduced energy demand

fewer CO2 emissions from fossil fuels

use reactions with better atom economy '

less undesired products and hazardous solvents and reactants

what is a maxwell distribution curve

a graph that shows the distribution of energies at a certain temparature

in a gas some particles will have very low energy, some very high, most in between

what happens to the Boltzmann distrinution curve in increasing temparatures

it flattens and the peak shifts to the right

dynamic equilibrium

the rate of the forward reaction is equal to the rate of the backward reaction in a closed system and the concentrations of each are constant

closed system

none of the reactants or products escape form the reaction mixture

open system

matter and energy can be lose to the surroundings

equilibrium position

relative akounts of products and reactants in an equilibrium mixture (to left is more reactants right more products)

Le Chatelier’s principle

if a change is made to a system in dynamic equilibrium the position of the equilibrium moves to counteract this change

equilibrium shift in concentration of reactant change

increse to right, decrease to left

equilibrium shift in pressure changes

increase shifts to direction with less gas molecules to decrease the pressure, decrease vice versa

effect of temparature on equilibrium

increase moves to endothermic side, decrease moves to exothermic

catalyst in dynamic equilibrium

increase the rate of the forward and backward reaction equally. only cause a reaction to reach equilibrium faster. no effect on position of equilibrium

the haber process

synthesis of ammonia with the equation

N2(g) + 3H2(g) ⇌ 2NH3(g)

maximising ammonia yield in the haber process

increase in pressure because there is less gas molecules but high pressure expensive so 200atm chosen

lowered temparature because exothermic reaction but too low not enough activation energy so compromise of 400-450c chosen

iron catalyst

the contact process

the synthesis of sulfuric acid with equation

2SO­₂ (g) + O₂ (g) ⇌ 2SO₃ (g)

maximising sulfuric acid yield in the contact process

increase pressure because les gas molecules but only carried out at 1atm because higher is unecessary and expensive

lowered temparature because reaction is exothermic but compromise of 450c is used

vanadium(V) oxide catalyst

the equilibrium constant expression

an expression that links the equilibrium constant, K to the concentrations of reactants and products at equilibrium taking the stoichiometry of the equation into account

how to write equilibrium constant expression

• Solids are ignored in equilibrium constant expressions

• The equilibrium constant, K, of a reaction is specific to a given equation

• The K_c of a reaction is specific and only changes if the temperature of the reaction changes

using Kc for equilibrium position

• The magnitude of K_c indicates the relative concentrations of reactants and products in the mixture

  • If K_c is very large (Kc >>1) the equilibrium lies to the RHS so the reaction mixture contains mostly products

  • If K_c is very small (Kc << 1) the equilibrium lies to the LHS so the reaction mixture contains mostly reactants

  • If K_c is close to 1 the mixture contains a similar concentration of both reactant and products

how is the periodic table arranged

-by increasing atomic number

-in periods showing repeating trends in physical and chemical properties (periodicity)

-in groups having similar chemical properties

s block elements

group one and two (because their electron configuration ends in s)

p block elements

groups 3-8 (because theirt electorn configuration ends in p)

d block elements

transition metals

first ionisation energy

the removal of 1 mol of electrons from 1 mol of gaseous atoms

lattice enthalpy definition ∆LEH

enthalpy change from the formation of 1 mol of an ionic lattice from gaseius ions

how can latttice enthalpy tell use the strength of bonds

higher enthalpy stronger bonds

enthalpy change of formation

the enthalpy change that occurs when 1 mole of the substance is formed from its elements in their standard states

enthalpy change of atomisation

ΔatH is the enthalpy change when one mole of gaseous atoms is formed from the element in its standard state, under standard conditions.

electron affinity

enthalpy changes when one mole of electrons is added to one mole of gaseous atoms/ions

enthalpy of solution

the enthalpy changfe when 1 mol of a solute dissolves ∆solH

enthalpy change of hydration

the enthalpy change when 1 mol of gaseous ions dissolves in water ∆hydH

factors affecting exothermic value of lattice enthalpy

-ionic charge - higher more attraction

-ionic radius - smaller more attraction

what is entropy

a measure of the dispersal of energy in a system which is greater the more disordered a system

when is a reaction thermodynamically stable

-absolute 0 (0K, maximum order)

-gibbs free energy is positive

change in entropy when melting

-increase - smaller than liquid to gas

change in entropy when boiling

-increase - larger than from solid to liquid

change in entropy when condensing or freezing

decrease

change in entropy when moles of gas increase

increase

change in entropy when number of gas moles decrease

decrease

Gibbs free energy equation

∆G = ∆H – T∆S

feasibility of positive ∆H negative ∆S

∆G always positive. never feasible

feasibility of negative ∆H positive ∆S

∆G always negative. reaction feasible

feasability of negative ∆H negative ∆S

∆G negative at low temp. feasible at low T

feasibility at positive ∆H positive ∆S

∆G negative at high temp, feasible at high T

what range must ∆G be for a reaction to be feasible

0 or less

limitations of predictions made for feasability

-decomposition of hydrogen peroxide gibbs is -117kJmol-1

-doesn’t decompose spontaneously. very high activation energy so reacts very slowly