C5 - MONITORING AND CON TROLLING CHEMICAL REACTIONS (9-1 SPECIFICATION)

• A solution is more concentrated when you dissolve more solute and when the molecules are more crowded. Standard solutions have set concentrations.
  

Concentration = solute mass ÷ solution volume

Titrations:

1. Measure a set volume of alkali into a flask and fill burette with acid. Add indicator to alkali.

2. Use burette to slowly add acid to alkali until the indicator changes colour.

The indicator changes colour when the acid has been neutralised so this shows the volume of acid needed to neutralise your alkali (the titre). Repeat and average results.

Concentration = no. moles ÷ solution volume

• The volume occupied by one mole of gas is the molar volume.

molar volume = gas volume ÷ no. moles

• At room temp. and pressure any mole of gas always occupies 24dm3

percentage yield = actual yield ÷ theoretical yield x 100

• Theoretical yield is the mass of product you'd make if all reactants were converted into products.
• A 100% yield means all reactant were converted to products and 0% yield means no reactants were converted to product.
• A reaction with low yield has lots of waste products which increases cost in industry.

atom economy = Mr of desired products ÷ Mr of all products x 100

• Atom economy tells you how much of the reactants has been converted into desired product. The higher it is, the greener to reaction.
• Reactions with low atom economies quickly use up resources and make lots of waste products. These reactions are unsustainable and unprofitable.
• The ideal reaction has useful by-products that don't need to be disposed of.

Reaction rate is dependent on collision frequency and energy transferred during collisions.

Temperature:

• Increased temp. means particles move faster and collide more often.
• Energy of collisions is also increased as particles move faster.
• More successful collisions at high temp., faster rate of reaction.

Concentration:

• More concentated solutions make collisions more likely which increases reaction rate.

Surface Area to Volume Ratio:

• Powders have a faster rate of reaction than large solids as more sides are available to collide with other substances. Increased rate of reaction for substances with a higher SA:V.

• Catalysts increase rate of reaction without being changed themselves.
• They function by decreasing activation energy by creating an alternative reaction pathway.

• You can identify if a suspected solid is a catalyst. Measure reaction rate with and without it and and weigh the solid before and after to ensure none was used up.

• Enzymes are biological catalysts that speed up reactions in living cells e.g. photosynthesis, respiration.

'⇌' shows a reversible reaction.

• Equilibrium is reached when the forward reaction occurs at the same rate as the backward reaction. Both reactions still occur but to no effect.
• This can only occur in a closed system where no reactants / products can escape.

• Temperature, pressure and concentration all affect the position of equilibrium.

Temperature:

• Increase temperature, equilibrium moves in exothermic direction to produce more heat.
• Decrease temperature, equilibrium moves in endothermic direction to absorb extra heat.

Pressure (only affects equilibria involving gases):

• Increase pressure, equilibrium moves to side with fewer gas moles to reduce pressure.
• Decrese pressure, equilibrium moves to side with more gas moles in increase pressure.

Concentration:

• Increase reactant concentration, equilibrium moves right to use up reactants and make more products.
• If you increase product concentration, equilibrium move left to use up products and make more reactants.