LC CHEMISTRY- RATES OF REACTION

REBECCA'S LC CHEMISTRY- RATES OF REACTION KNOWT

rate of reaction

change in concentration PER unit time

instantaneous rate

rate of a reaction at any specific moment

activation energy

minimum energy required for particles to react

effective collision

where particles have enough energy to react

nature of reactants

• ionic reactants react faster as their bonds are already broken in water

• covalent reactants react slower as bonds must break first

particle size

smaller particle size increases reaction rate by increasing surface area and collisions

catalyst

substance that changes reaction rate without being used up

homogeneous catalysis

catalyst and reactants are in the same phase no boundary between them

heterogeneous catalysis

catalyst and reactants are in different phases

enzyme 2 examples

• catalase breaks down H₂O₂

• lysozyme breaks down bacterial cell walls

catalytic converters

use platinum palladium rhodium to convert CO and NO into CO₂ and N₂

dust explosion

requires

• combustible dust

• air

• confined space

• ignition

exothermic reaction

reaction that releases heat

endothermic reaction

reaction that absorbs heat

effect of temperature

increased temperature raises reaction rate by providing more particles with activation energy

effect of concentration

higher concentration increases rate due to more collisions

properties of a catalyst

• specific

• needed in very small amount

• can be poisoned by certain substances

intermediate formation theory (homogenous catalysis)

• one reactant reacts with catalyst to form an intermediate compound

• intermediate is unstable exists for a very short time

• intermediate reacts with other reactant, forming product and regenerated catalyst

intermediate formation theory (homogenous catalysis) example

• potassium sodium tartrate and cobalt (II) catalyst mixed together.

• solution is pink due to cobalt (II).

• hydrogen peroxide added

• fizzing seen solution turns green

• green colour is due to formation of cobalt (III), our intermediate

• fizzing stops solution turns pink again

• producs are now formed

• cobalt (II) catalyst has been regenerated

surface absorption theory (heterogeneous catalysis)

reactant adsorbed onto surface of catalyst forming new stronger bonds between each other product diffuses away

surface absorption theory (heterogeneous catalysis) example 1

hydrogen gas and oxygen gas react quickly to form water vapour on the surface of a platinum catalyst

Name three of the metals used as catalysts in catalytic converters.

• platinum

• palladum

• rhodium

explain how catalysts increase the rate of reaction

providing alternative reaction pathway with a lower activation energy

Name a substance that could 'poison' the catalysts of the catalytic converter

lead compounds

Explain how the type of bonding in the reactants influences the rate of a chemical reaction in aqueous solution

ionic compound react quickly as dissociated as only ions need to collide

How could you reduce the rate of a reaction that takes place in solution?

• lower concentration

• temperature

• inhibitor

inhibitor

negative catalyst

state one observation made during the oxidation of methanol using platinum wire as a catalyst

• wire glows

• odour smell of methanol

• popping

• flask becomes hot

• methanol boils

• methanol used up

identify two major products of the oxidation of methanol

water

hydrogen

what term is usually used to describe the attachment of liquid or gaseous molecules to a solid surface?

absorption

explain how the interaction between methanol and the platinum catalyst affects the rate of oxidation

lower activation energy

explain how a catalyst poison like sulfur interferes with a catalyst

surface active sits blocked minimum energy for effective collisions

give another example of a reaction which involves the same type of catalysis, indicating clearly the reactant(s) and the catalyst

hydrogen and oxygen and platinum

effect of an increase of temperature on number on collisions

small increase

effect of an increase of temperature on effectiveness of collisions

large increase

effect of an increase of temperature on activation energy

none

state way to increase collisions

increase temperature

suggest a reason why chemical would not formed in every collision between a pair of (other chemical)

did not possess enough activation energy

state a way to increase the frequency of collisions

increase temperature

define rate of chemical reaction

change in concentration per unit time

give reason why the rate of a chemical reaction increase when temperature increases

particles move faster with higher energy more effective collisions

give reason why the rate of a chemical reaction increase when concentration increases

more molecules more effective collisions

give reason why the rate of a chemical reaction increase when particle size decreases

smaller particle size means greater surface area on which collisions occur more effective collisions

explain how the catalyst in the catalytic converter works

hot harmful gases absorbed onto the surface catalyst converted to less harmful gases and removed

which theory best describes the catalytic converter process

adsorption theory

effective collision

collision which causes reaction

how can a catalyst lower activation energy of a reaction

provides alternative pathway

suggest a reason why chemical reactions are generally slow when the reactants are kept together in the solid state

purchase small quantities

what chemical hazard is indicated by the pictogram?

oxidising

give one safety precaution that should be taken when using or storing hydrogen peroxide solutions

wear PPE

describe the appearance of the MnO₂ catalyst

brown solid

describe the appearance of the S₂ catalyst

yellow