C2b Flashcards
(43 cards)
Collision/Particle theory
A reaction occurs when particles collide with enough energy/speed (Activation Energy, Ea) to react.
The more collisions per second, the higher the rate.
Rate
A measure of how fast a reaction proceeds.
Activation Energy, Ea
The minimum amount of energy required in a collision for particles to react.
What are the 4 factors that the rate of reaction depends on?
1) Temperature: if you increase the temp, particles move faster, so particles have more energy, so increased collisions, so increased rate.
2) Concentration (pressure): if you increase concentration: more particles, so more collisions, so increased rate.
3) Surface area: if you increase the surface area, more particles available to collide, so more collisions, so increased rate.
4) Catalyst:
• Lowers the Ea requires for a successful collision, so increased successful collisions, so increased rate.
• It provides a “site”/surface for particles to “stick” to. Increased the frequency of collisions, so increased rate.
What are the advantages, and disadvantages of catalysts?
Advantages:
• They reduce the temperature required for a successful reaction. This saves energy, time, and money.
Disadvantages:
• They are reaction-specific: you need a different one for each reaction.
• Very expensive.
• They can be destroyed/poisoned by impurities in a reaction.
Rate (equation)
Rate = Amount of reactants (or products)/Time
On a graph:
• The steeper the gradient, the quicker the rate (because of temp/SA/catalyst)
• The different rates should all level out at the same point (when all the reactants are used up). If there is a line that continues reacting, it had more reactants (higher concentration).
Precipitate, ppt
Insoluble solid (doesn’t dissolve).
Insoluble
Doesn’t dissolve
Measuring rate: Precipitation reactions
(See diagram) Rate can be calculated by how quickly the X disappears.
• The quicker it disappears, the quicker the reaction.
• Make sure the same person does it each time (eyesight- some may see through cloudiness quicker).
Measuring rate: Change in mass
(See diagram) Rate can be measured by timing how quickly mass falls.
• The quicker the mass falls, the quicker the reaction.
• Caution: gas is released into the room (do in a fume cupboard)
• This is very accurate.
Measuring rate: Volume of gas given off
(See diagram) Rate can be measured by how quickly a fixed volume of gas is produced.
• More gas given off = faster reaction
• Caution: if the reaction occurs too quickly it could disconnect the gas syringe… explode.
• Gas syringes are quite accurate (to nearest mm)
Examples of reaction rate experiments
1) Temperature:
Sodium Thiosulphate + Hydrochloric acid -> Sodium Chloride + water + sulphur
2) Concentration:
Magnesium + Hydrochloric acid -> Magnesium chloride + hydrogen
3) Surface area:
Hydrochloric acid + Calcium Carbonate -> Calcium Chloride + Carbon Dioxide + water
4) Catalyst: Hydrogen Peroxide (+ catalyst: Magnesium (IV) oxide) -> water + oxygen
Exothermic reaction
Heat energy is transferred to surroundings (temp rises) from the bonds.
e.g. Combustion (burning fuels), Neutralisation (acid + alkali), Oxidation reactions (e.g. Na + H2O)
Uses: handwarmers, self-heating coffee cans
Endothermic reaction
Heat energy is taken in from the surroundings (temp falls), and converted into bond energy.
e.g. Thermal decomposition (e.g. CaC03 -> CaO + CO2)
Uses: ice packs (for sports injuries)
pH scale
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Strong acid. Weak acid. Neutral. Weak acid. Strong alkali.
Indicator
A substance that changes colour depending on the pH e.g. Universal Indicator (Reds, oranges, and yellows for acids. Green for neutrals. Blues, and purples for alkalies)
Base
A substance with a pH greater than 7.
An alkali is a base that dissolves in water.
Acid + Base -> ?
Acid + Base -> Salt + water
e.g. HCl + NaOH -> NaCl + H2O
What ions do acids contain? What ions do alkalies contain?
Acids contain H+ ions e.g. H+Cl
Alkalies contain OH- ions e.g. NaOH-
Hydrochloric, Sulphuric, and Nitric acid
Acid: Formula: Salt made:
Hydrochloric HCl Chloride
Sulphuric H2SO4 Sulphate
Nitric HNO3 Nitrate
Acid + Metal -> ?
Acid + Metal -> Salt + Hydrogen
e.g. 2HCl + Mg -> MgCl2 + H2
- Any metal below Hydrogen in the reactivity series will not react.
- Metals high up in the reactivity series are too reactive, and will explode e.g. K, Na
Neutralisation reactions:
Acid + Metal oxide/hydroxide -> ?
Acid + Metal oxide/hydroxide -> Salt + water
e.g. 2HCl + CuO -> CuCl2 + H2O
Haber process (neutralisation reaction)
Ammonia(g) + Nitric acid(aq) -> Ammonium nitrate(s)
NH3 + HNO3 -> NH4NO3
- Very important industrial reaction as it produces fertiliser (ammonium nitrate)
- This is a rare neutralisation reaction that doesn’t produce water, just the ammonium salt.
- Uses an iron catalyst.
Making soluble salts using Metals, Metal oxides, or Metal hydroxides (neutralisation reaction)
M/MO/MOH + Acid -> Salt + water
e.g. 2HCl + CuO -> CuCl2 + H2O
Method:
• Add excess M/MO/MOH to your acid (to make sure all acid is used up), and stir to dissolve, and react to form a salt.
• Filter out the excess M/MO/MOH.
• Allow the H2O to evapourate, leaving the salt.
