Chemical Reactivity

define: surface area

a measure of the proportion of particles on a surface of a substance that are exposed and so able to react

(will purely affect the frequency of collisions)

describe: increasing surface area effect on reaction

increasing surface area (using powder form)

-means proportion of particles that are exposed and able to react is increased

-this leads to an increase in the frequency of collisions

-as a result, this means that there is an increase in the frequency of successful collisions

-however the proportion of successful collisions remains the same

-leads to an increase in the rate of reaction

define: catalyst

provides an alternate reaction pathway with lower activation energy, without being used up

describe: catalyst effect on reaction

since it provides an alternate reaction pathway, without being used up

-means activation energy is lower

-means that the proportion of particles that have sufficient kinetic energy to overcome activation energy barrier will increase

-thus, there is an increase in the frequency of successful collisions

-leads to an increase in the rate of reaction

define: temperature

the measure of the average kinetic energy of the particles inside a substance

describe: increase in temperature effect on reaction

increase in temperature

-means that the average kinetic energy of particles will increase

-particles are moving faster

-there is an increase in the frequency of collisions occurring

-also means that a higher proportion of particles will have sufficient kinetic energy to overcome the activation energy barrier

-means there is an increase in the frequency of successful collisions

-the rate of reaction is increased

define: concentration

a measure of the amount of particles per unit of volume

describe: increase in concentration effect on reaction

increasing the concentration:

-means there will be in an increase in the number of particles in a set space

-lead to an increase in the frequency of collisions

-leads to an increase in the frequency of successful collisions

-however, proportion of collisions that are successful remain the same

-rate of reaction is increased

describe: collision theory

states that in order for a reaction between two particles to occur:

-particles must collide with the correct orientation

-particles must have sufficient kinetic energy to overcome the activation energy barrier

describe: dynamic equilibrium

when the forward and reverse reactions have the same rate, and so there is no ret reaction, or change in the system

describe: conditions needed for dynamic equilibrium to be established

-can only exist in a closed system (so no reactants/products can escape)

-can only occur with reversible reactions

-must be held at a constant temperature and pressure

-the concentrations of substances do not change (but may not necessarily be the same)

describe: what Kc value means

if Kc is greater than 1: at equilibrium, the reaction will favour the products, so there will be more products than reactants

if Kc is less than 1: at equilibrium, the reaction will favour the reactants, only a small amount of product is formed, more reactants than products

describe: what Qc value indicates

Qc= represents the calculated value for an equilibrium reaction that has not reached equilibrium yet

-if Qc is larger than Kc, the reaction will proceed in reverse (increase in reactants) until equilibrium is established (rate of forward + reverse is equal)

-if Qc is smaller than Kc, the reaction will proceed forward (increase products) until equilibrium is established (rate of forward + reverse is equal)

what is the only thing that can change Kc?

temperature is the only thing that can change this value

describe: effects of pressure

increase in pressure, means a decrease in volume= system will act to oppose change, favouring side with fewer number of gaseous moles to decrease the number of gas particles to re-establish equilibrium

decrease in pressure, means an increase in volume= system will act to oppose the change, favouring the side with largest number of gaseous moles, to increase the number of gas particles to re-establish equilibrium

-does not affect the value of Kc

describe: effects of temperature

increase in temperature, means heat is being added= system will favour the endothermic reaction, absorbing the increased heat energy supplied to the system to re-establish equilibrium

decrease in temperature, means heat is being removed= system will favour the exothermic reaction, releasing heat energy to re-establish equilibrium

describe: effects of pressure where number of gaseous moles is the same

a change in pressure will have no effect on the equilibrium position

describe: what side reaction favours with increasing/decreasing Kc

increasing Kc- will favour the products

decreasing Kc- will favour the reactants

describe: le chatalier's principle

states that when an equilibrium is stressed, it will respond by moving in the opposite direction to minimise the change

describe: effects of concentration

increase in concentration, extra product/reactant being added to mixture= reaction will favour the other side of the reaction, to use up some of added substance to re-establish equilbrium

decrease in concentration, reactant/products being removed from mixture= reaction will favour side of that material, to produce more of the removed substance to re-establish equilibrium

describe: effects of catalyst

provides alternate reaction pathway with lower activation energy

-higher proportion of particles have sufficient kinetic energy to overcome activation energy barrier

-reaction is faster

-both the forward and reverse reactions are affected the same way

-allows equilibrium to be established more quickly, but no change in the position of equilibrium

define: acid and base + reaction

acid= donates protons

base= accepts protons

acid-base reaction= one in which a proton is transferred from an acid to a base

what is Kw?

-is the dissociation constant/ionic product of water

1 x 10⁻¹⁴

describe: exothermic reaction in relation to activation energy

total energy released is greater than the activation energy for the reaction

-energy released by initial exothermic reaction is used to provide activation energy for other particles to react

-once exothermic reaction begins, it will continue until one of the reactants is used up or some other change occurs

describe: endothermic reaction in relation to activation energy

energy released is less than the activation energy for the reaction

-these reactions have a different driving force which allows colliding particles to gain sufficient activation energy

describe: the two main ways rate of reaction can be increased

-increasing the frequency of collisions occurring (surface area, concentration and temperature)

-increasing the energy of the collisions, so more collisions are effective (temperature, catalyst)

describe: ionisation/dissociation

-the transfer of hydrogen ions (since ions are formed)

state: ways to define acids

-damp blue litmus paper turning red

-hydrogen gas is released when a metal is added (with pop sound when ignited in air)

-carbon dioxide gas is released when calcium carbonate is added (becomes milky when passed through limewater)

state: ways to define bases

-damp red litmus paper turning blue

-ammonia gas is released when added to a warmed ammonium compound (smell/turns litmus blue)

define: amphiprotic

-it can act as a proton donor in neutral/basic conditions

-it can act as a proton acceptor in acidic conditions

define: strong acid + properties

dissociate completely in water

-have a low pH

-react rapidly with magnesium ribbon

-are good conductors of electricity

define: weak acid + properties

partially dissociate in water

-have a pH less than 7 but seldom below 3

-react slowly with magnesium ribbon

-are poor conductors of electricity

define: strong bases +properties

completely dissociate in water

-have a high pH

-react rapidly with ammonium compounds to release ammonia gas

-are good conductors of electricity

define: weak bases + properties

only react to a small extent with water

-have a pH above 7 but seldom above 11

-react slowly with ammonium compounds to release ammonia gas

-are poor conductors of electricity

state: common strong acids

HNO₃

HCl

H₂SO₄

HBR

state: common weak acids

NH₄⁺

CH₃COOH

CHOOH

HF

CH₃NH₃⁺

HCN

state: common weak bases

NH₃

CH₃COO⁻

CHOO⁻

F⁻

CH₃NH₂

CN⁻

state: common strong bases

NaOH

KOH

S²⁻

state common salts

NH₄Cl

CH₃COONa

CH₃NH₃Cl