Chemistry: Topic 2 & 1.3

volumetric analysis and managing chemical processes

limiting reagents

whichever reactant has less mols.

collision theory

reactants must collide for chemical reactions to occur.

successful collisions: particles must have sufficient energy and orientation to react and form products.

unsuccessful collisions: particles collide but bounce off each other without a reaction occurring.

activation energy

the minimum energy required for a chemical reaction to occur

when does the rate of reaction speed up

the rate of reaction will speed up if:

• the frequency of collisions increases

• the proportion of successful collisions increases

average rate of change formula

y2-y1/x2-x1

measures the change in quantity being measured over a defined period of time.

instantaneous rate

• measure of the rate at a particular instance

• represented as the slope of the tangent

tangents

steep tangent: fast rate of reaction

shallow tangent: slow rate of reaction

zero gradient: reactants have stopped converting to products.

Explain the effect of higher temperatures on the rate of the chemical reaction

at a higher temperature, the reacting particles have increased average kinetic energy. this increases the number of collisions per unit time. A greater proportion of reacting particles reach or exceed the activation energy and collide in the correct orientation. This increases the number of successful collisions.

Explain the effect of higher pressure on the rate of the chemical reaction

at a higher pressure, there are more mols of gaseous particles per unit space . this increases the number of collisions per unit time. A greater proportion of reacting particles reach or exceed the activation energy and collide in the correct orientation. This increases the number of successful collisions.

Explain the effect of increased surface area on the rate of the chemical reaction

increased surface are increases the number of sittes for collision to occur. . this increases the number of collisions per unit time. A greater proportion of reacting particles reach or exceed the activation energy and collide in the correct orientation. This increases the number of successful collisions.

Equilibrium

occurs when the rate that reactants are being converted to products is the same as the rate where products are being converted to reactants.

characteristics of equilibrium

1. closed system: no matter is lost to surroundings

2. dynamic process: neither forwards or backwards reactions ever stop

3. rate of forwards and backwards reactions are equal

4. amount of reactants/products at equilibrium remains constant: no observable change.

when does the Kc value change

• temperature

Le Châtliers principle

if an external change is made to the system, the change will be counteracted.

Le Châtliers (wording)

according to le châtliers principle, the system will attempt to counteract the increase in XYZ by decreasing XYZ. this favours the forwards/backwards reaction, shifting eq position to the right/left

1. identify change

2. state le chatliers

3. outcome

pressure graph

temperature graph

• gradual increase/decrease

optimising production

Yield

quantity of product formed during a process, referring to the efficiency of the system.

theoretical: quantity expected from stoichiometric calculations

actual: quantity obtained through chemical process

percent: % ratio comparing actual to theoretical

%yield= actual/theoretical x100