TOPIC 7 – Chemical Reactions
· PHYSICAL AND CHEMICAL CHANGES:
- Physical Changes = no new substances are made but the appearance of a substance changes.
- Examples: bubbles, colour changes or changes of state.
- Chemical Changes = a process of rearrangement of atoms in the reactants to form new products, they
have the same number of atoms and types but they are in different forms.
- Examples: neutralisation reactions to form salts or rusting.
· RATE OF REACTION:
- Factors that affect it:
· REVERSIBLE REACTIONS:
- These are the reactions that can be reversed. (i.e. an ice cube, freeze water to make it, melt to reverse).
- Effects on some examples:
· THE EQUILIBRIUM CONCEPT:
- This refers to when the rate of the forward reactions equals the rate of the reverse reaction because
then overall the reactions is in a state of equilibrium.
- The relative amounts of all the reacting substances at equilibrium depend on the conditions of the
reaction.
- If a system is at equilibrium and a change is made to any of the conditions, then the system responds
to counteract the change.
- When a reversible reaction occurs in a closed system, equilibrium is reached when the reactions
occur at exactly the same rate in each direction.
· EFFECTS OF CHANGING CONCENTRATION, PRESSURE & TEMPERATURE:
- Concentration = if the concentration of a reactant or product changes, the reaction is no longer at
equilibrium and the concentrations will change until the reactions is back to equilibrium again.
- Pressure = in gaseous reactions, an increase in pressure will favour the reaction that produces the
least number of molecules as shown by the symbol equation for that reaction.
- Temperature = if temperature is increased, equilibrium moves in the direction of the endothermic
reaction. If temperature is decreased, equilibrium moves in the direction of the exothermic reaction.
· PHYSICAL AND CHEMICAL CHANGES:
- Physical Changes = no new substances are made but the appearance of a substance changes.
- Examples: bubbles, colour changes or changes of state.
- Chemical Changes = a process of rearrangement of atoms in the reactants to form new products, they
have the same number of atoms and types but they are in different forms.
- Examples: neutralisation reactions to form salts or rusting.
· RATE OF REACTION:
- Factors that affect it:
· REVERSIBLE REACTIONS:
- These are the reactions that can be reversed. (i.e. an ice cube, freeze water to make it, melt to reverse).
- Effects on some examples:
· THE EQUILIBRIUM CONCEPT:
- This refers to when the rate of the forward reactions equals the rate of the reverse reaction because
then overall the reactions is in a state of equilibrium.
- The relative amounts of all the reacting substances at equilibrium depend on the conditions of the
reaction.
- If a system is at equilibrium and a change is made to any of the conditions, then the system responds
to counteract the change.
- When a reversible reaction occurs in a closed system, equilibrium is reached when the reactions
occur at exactly the same rate in each direction.
· EFFECTS OF CHANGING CONCENTRATION, PRESSURE & TEMPERATURE:
- Concentration = if the concentration of a reactant or product changes, the reaction is no longer at
equilibrium and the concentrations will change until the reactions is back to equilibrium again.
- Pressure = in gaseous reactions, an increase in pressure will favour the reaction that produces the
least number of molecules as shown by the symbol equation for that reaction.
- Temperature = if temperature is increased, equilibrium moves in the direction of the endothermic
reaction. If temperature is decreased, equilibrium moves in the direction of the exothermic reaction.
