Rates of Reaction and Chemical Equilibrium Concepts

Collision theory

Chemical reactions can occur only when reacting particles collide with each other and with sufficient energy.

Activation energy

The minimum amount of energy that particles must have to react.

Factors that affect the rate of a reaction

Concentration, Temperature, Pressure, Catalyst, Surface area.

Equipment needed to measure the rate of reaction

Stop clock, Balance or measuring cylinder/gas syringe.

Loss of mass of the reactants

Use a balance to measure the loss of mass.

Volume of gas produced

Use a gas syringe or upturned measuring cylinder to measure the volume of gas produced.

Time taken for the solution to become cloudy

Place conical flask on cross and watch it disappear.

Rate calculation at a specific time

Rate = change in mass / change in time.

Average rate calculation

Rate = change in y / change in x.

Gradient calculation

Gradient = change in y / change in x.

Rate example calculation

Rate = (3.1 - 1.4) / (120 - 30) = 0.0189 /s.

Steeper curve on rate graphs

Indicates a faster rate of reaction.

Horizontal line on graph

Indicates that the reaction is finished and reactants are used up.

Limiting factor

Reaction stops due to a limiting factor.

Closed system

When reactants or products cannot enter or leave the system.

Catalysts

Increase the rate of reaction by providing a different pathway for the reaction that has a lower activation energy.

Equilibrium definition

The rate of the forward and reverse reaction is the same, and the concentrations of reactants and products are constant.

Le Chatelier's principle

Use to explain the effect of changing the conditions on the position of equilibrium.

Biological catalyst

Enzyme.

Effect of temperature on equilibrium

Increase in temperature - reaction moves in the endothermic direction; Decrease in temperature - reaction moves in the exothermic direction.

Effect of pressure on equilibrium

Increase in pressure - reaction moves to the side of the fewer moles; Decrease in pressure - reaction moves to the side of the most moles.

Effect of concentration on equilibrium

Increase in concentration of a chemical - reaction moves to the opposite side to use up excess chemical; Decrease in concentration - moves to this side to create more of this chemical.

Reversible reaction example

Anhydrous copper sulfate + water → Hydrated copper sulfate.

Effect of a catalyst on equilibrium

No effect on the position of equilibrium; allows the reaction to reach equilibrium faster.

Evolution of the Atmosphere

Methane reacted with oxygen to form carbon dioxide and water; Volcanoes released water vapour, carbon dioxide, methane, ammonia.

Today's atmosphere composition

78 % Nitrogen (N2), 21 % oxygen (O2), 1 % other gases.

Reasons why O2 levels increased

Oxygen levels increased, allowing animals to evolve; Absorbed by oceans.

Reasons why CO2 levels decreased

Locked up as sedimentary rocks and fossil fuels; Used in photosynthesis to produce oxygen.

Formation of coal

Carbon dioxide was used during photosynthesis by trees; Trees die and are compressed over millions of years.

Greenhouse Gases

Water vapour (H2O), Carbon dioxide (CO2), Methane (CH4) that trap heat in the atmosphere.

Effects of Global Climate Change

Includes sea level rise, more frequent and severe storms, changes to wildlife distribution, and increased temperatures.

Human Activities Which Increase Greenhouse Gases

Combustion of fossil fuels, deforestation, and increased animal farming contribute to higher greenhouse gas emissions.

Carbon Footprint

The total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event.

How to Reduce the Carbon Footprint

Increased use of alternative energy supplies, energy efficient appliances, carbon capture and storage (CCS), and lifestyle changes.

Problems on Reducing the Carbon Footprint

Economic considerations such as the affordability of building more wind turbines.

Sulfur dioxide (SO2)

Formed from sulfur in fossil fuels reacting with oxygen; causes respiratory problems and acid rain.

Carbon monoxide (CO)

Produced from incomplete combustion of hydrocarbons; a toxic gas that can cause death.

Carbon particulates (unburned hydrocarbons)

Solid particles resulting from incomplete combustion that can harm health and the environment.

Oxides of nitrogen (NOx)

Formed from nitrogen and oxygen reacting at high temperatures; causes respiratory problems and acid rain.

Mole

Mole = mass (g) / relative formula mass.

Avogadro's Number

6.02x10^23, the number of particles in one mole of a substance.

Volume

Volume in dm3 is calculated by dividing cm3 by 1000.

Concentration

Concentration (g/dm3) = mass (g) / volume (dm3).

Limiting Reactants

The reactant that is completely used up in a reaction, limiting the amount of products formed.

Theoretical Yield Calculation

The mass of product expected from a reaction based on the limiting reactant.

Example of Limiting Reactants

In the reaction 2H2O2 → 2H2O + O2, the limiting reactant is determined by comparing moles.

Mass of Oxygen Produced

128 grams of hydrogen peroxide breaks down into water and oxygen.

Moles Calculation

Moles = mass / relative atomic mass; for example, 3 g of Mg reacts with 7 g of O2.

Reaction Ratio

The ratio of reactants and products in a chemical reaction, such as 2H2O2 : 1O2.

Final Reaction Completion

Once the limiting reactant has reacted, the reaction is complete.

Photosynthesis

The process by which trees use carbon dioxide to produce oxygen and reduce global warming.

Decomposition of Rubbish

Leads to increased methane emissions from landfill sites.

Animal Farming

Contributes to methane emissions through digestion and waste decomposition.

Balanced Equation

The equation representing the reactants and products in a chemical reaction with equal numbers of atoms for each element.

Moles of Reactants and Products

The quantity of a substance measured in moles, used to balance chemical equations.

Alkane

A hydrocarbon made of C-C single bonds.

Alkane General Formula

Cn H2n + 2, where n is the number of carbon atoms.

Homologous Series

A family of hydrocarbons with similar chemical properties who share the same general formula.

Fractional Distillation

A process to separate mixtures based on different boiling points.

Boiling Point

The temperature at which a liquid turns into a gas.

Flammability

How easily a substance ignites (catches on fire).

Viscosity

The runniness of a liquid; higher viscosity means longer flow time.

Volatility

How easily a liquid changes into a gas.

Incomplete Combustion

A reaction with insufficient oxygen, producing carbon monoxide and water.

Complete Combustion

A reaction with sufficient oxygen, producing carbon dioxide and water.

Cracking

The process of breaking down hydrocarbons into smaller, more useful molecules.

Thermal Decomposition

Breaking down a compound using heat.

Catalytic Cracking

Cracking that requires a catalyst and high temperature.

Steam Cracking

Cracking that uses high temperature and steam.

Alkene

A hydrocarbon made of C=C double bonds.

Chemical Test for Alkene

Add bromine water; alkene turns from orange to colourless.

Test for Carbon Dioxide

Bubble through limewater; result turns cloudy.

Fossil Fuels

Non-renewable fuels such as coal, crude oil, and natural gas.

Combustion

Burning in oxygen.

Fraction

Molecules with a similar number of carbon atoms.

Reaction Conditions

The specific conditions under which a chemical reaction occurs.

Carbon Monoxide

A toxic gas produced during incomplete combustion.

Gas

Chemical test

Hydrogen (H2)

Lit splint; Pop sound

Oxygen (O2)

Glowing splint; Splint relights in oxygen.

Formulation

A mixture that has been designed as a useful product e.g. shampoo.

Carbon Dioxide (CO2)

Turns milky/cloudy when bubbled through limewater.

Chlorine (Cl2)

Damp litmus paper; Paper is bleached (white).

Pure water

Boil it; Boils at exactly 100 oC.

Melting point

The temperature at which a solid turns into a liquid. Ice has a melting point of 0 oC.

Chromatography

Can be used to separate mixtures and identify substances. Relies on the difference in solubility of the mixture.

Mobile phase

The solvent e.g. water running up the chromatogram.

Stationary phase

The paper used in chromatography.

Rf value

Tells you how far the substance has moved, relative to the solvent. Rf = distance moved by substance / distance moved by solvent. Rf value will always be less than 1.

Potable water

Safe to drink. Contains low levels of dissolved salts and microbes. Not pure.

Finite resource

A source from the Earth that is running out e.g. coal, crude oil.

Renewable source

A source that isn't running out e.g. wood.

Distillation

Method to obtain potable water from salty water by heating, evaporating, cooling, and condensing.

Sterilising agents

Chlorine, ozone, or ultra-violet light used to kill microbes.

Life Cycle Assessments (LCAs)

To assess the environmental impact of the stages in the life of a product.

High grade copper ore

Rock that contains enough copper that makes it economically viable to extract.

Low grade copper ore

Extract using phytomining or bioleaching.

Bioleaching

Uses bacteria to produce leachate solutions that contain metal compounds.

Saving Resources

Limits the use of raw materials, energy consumption, waste and environmental impacts.

Reuse

Use the item for another purpose e.g. a glass bottle is refilled.