Molecular interactions and reactions

When energy is released from the system

When the reactants have more potential energy than the products and the excess is released via heat or light (exothermic)

System of a chemical reaction

The collection of atoms or molecules involved in change. Usually a chemical reaction

Surroundings

Anything that is present around the atoms and molecules

Exothermic reactions

A change where energy is released from the system to the surroundings. Enthalpy of the system is reduced

Endothermic reactions

A change where energy is absorbed into the system from the surroundings. Enthalpy of the system is increased

Enthalpy

Stored chemical potential energy within a substance

Effect of endothermic reactions on surroundings

Temp OFTEN increases

Effect of endothermic reactions on surroundings

Temp OFTEN decreases

Exothermic changes of state

Condensation, freezing, deposition

Endothermic changes of state

Evaporation, melting, sublimation

Energy equation

A+B —> C + D + E (50J)

Energy equation

E (50J) + E + F —> G + H

Exothermic enthalpy association

Decrease of enthalpy in a system

Endothermic enthalpy association

Increase of enthalpy in a system

Stored potential energy dependance

The number and strength of the bonds in a substance

Exothermic reactions greater potential energy

Reactants

Exothermic reactions lesser potential energy

Products

Endothermic reactions greater potential energy

Products

Exothermic reactions lesser potential energy

Reactants

Delta H formula

Products - reactants

Endothermic reactions H value

Positive

Exothermic reactions H value

Negative

Baking a cake

Endothermic (BAC)

Making Jelly

Endothermic (MJ)

Cellular respiration

Exothermic

Methods of determining reaction rate

Rate which reactants disappear, rate at which products appear.

Reaction between CaCO3 and HCl (Products CaCl2, CO2, H2O)

Mass of CaCO3 will decrease, the concentratio of H+ ions will decrease, The volume of CO2 gas will increase, The concentration of Ca2+ ions will increase

Rate of reaction formula

Amount of substance used or produced/time taken

Slowest reaction rate

C

Fastest reaction rate

A

Most product formed

A

Nature of reactants

No complex bonding - fast, complex bonding - slow

Concentration of reactants

Gases or aqueous solutions - more particles per unit volume, more collisions

State of subdivision

Solids or liquids - Particles get smaller, SA increases, more likely to contact other reactants.

Temperature

All reactions - Particles move faster and with more kinetic energy. Collision is more likely to occur with enough energy to disrupt bonds.

Catalysts

Increases RR without permanent consumption - Alternative pathway with lower activation energy.

Collision theory

The theory that best describes how the RR can be affected by different factors.

1. Molecules must collide with enough energy to disrupt bonds

2. Molecules must collide with a suitable orientation for bond formation and breaking

Favourable orientation

.

Unfavourable orientation

.

Energy profile diagram

Energy distribution diagram

Equal factors

Slower reactions will have higher Ea than faster reactions

Kinetic theory

Increase in temp means an increase in the average kinetic energy of the particles

Haber-Bosch process

Process to produce Ammonia with the catalysts Fe/FeO

Contact process

Process to produce Sulphuric acid with the catalysts V2O5

Margarine process

Process to produce margarine with the catalysts Pt/Ni