Chemistry - Chemical Reactions

Synthesis reactions

a combination reaction of two substances to produce a new substance

A + B → AB

Decomposition

a decomposition reaction is the breaking up of a single compound into simpler substances

AB → A + B

Hydrocarbon Combustion

A reaction of a fuel with oxygen, producing energy in the form of heat and/or light

Fuel + O₂ → H₂O + CO₂

Displacement Reactions

a variety of reactions but all follow a general theme, like:

• Metal Displacement and acid-metal reactions (Single replacement) are: AC + B → AB + C

• Neutralisation and precipitation reactions (double replacement) are: AD + BC → AC + BD

Metal Displacement (Single replacement)

Occurs when a more reactive metal replaces a less reactive metal from its compound

A + BC → AC + B

Neutralisation Reaction (double replacement)

A neutralisation reaction is a reaction between an acid and a base to form a salt and water

AD + BC → AC + BD

acid + base → salt + water

Acid-metal reactions

occurs when an acid reacts with a metal to produce a salt and hydrogen

A + BC → AC + B

acid + metal → salt + hydrogen

Precipitation reactions

the mixing of two solutions to produce a solid. The solid is called a precipitate

solution + solution → solid + solution

Exothermic reaction

A chemical reaction that transfers energy (usually heat energy) to its surroundings.

Endothermic reaction

A chemical reaction that takes energy (usually heat energy) from its surroundings.

Exothermic

heat is released (feels warm)

Endothermic

heat is absorbed (feels cold)

How does exothermic reactions occur?

reaction occurs spontaneously

How does endothermic reactions occur?

energy must be added for reaction to occur

Exothermic reaction equation

Reactants → Products + Energy

Endothermic reaction equation

Reactants + Energy → Products

What is a rate of reaction?

the speed at which a chemical reaction occurs

• Reaction rate = Quantity of reactant used up / time

OR

• Reaction rate = Quantity of product formed / time

Collision theory

explains how chemical reactions occur and why reaction rates differ.

What does collision theory state?

• Particles must collide for a reaction to happen

• Only effective collisions ( with enough energy and correct orientation) lead to chemical change

What happens to the particles and reaction in a dilute solution? (concentration)

particles spread out → fewer collisions → slower reaction

What happens to the particles and reaction in a concentrated solution? (concentration)

particles are closer together → more collisions → faster reaction

What happens to the particles and reaction with higher pressure ? (pressure)

gas particles are closer together → more collisions -. faster reaction

What happens to the particles and reaction with lower pressure? (pressure)

particles are further apart → fewer collisions → slower reaction

Which state does pressure affect most?

pressure affects gasses but has little effect on solids and gasses.

• increasing the pressure on gasses makes collisions more likely

Which state does surface are affect?

reactants that are solid only then surface particles can react.

• breaking it into smaller pieces increases the surface area

What happens to the particles and reaction more surface area? (surface area)

more exposed particles → more collisions → faster reaction rate

What are the effects of stirring/ mixing? (agitation)

• increases particle motion

• Boots collision frequency

• Helps maintain or increase reaction rate

What happens to the particles and reaction with a hotter substance? (temperature)

faster particles → more collisions/ energetic collisions → faster reaction

What happens to the particles and reaction with a colder substance? (temperature)

slower particles → fewer collisions → slower reaction rate

What does a catalyst do?

It speeds up a reaction but is not used up. Catalyst lower the energy needed and make it easier for particles to react.

What is an Inhibitor?

It is the opposite of at catalyst, slows down a chemical reaction.