C2b Flashcards
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.
Making soluble salts using acid + alkali (neutralisation reaction)
Acid + Alkali -> Salt + water
Method:
• Add exactly the right amount of acid to alkali (using Universal Indicator to indicate exact neutralisation)
• Repeat with the same volume of acid to alkali, but without UI to avoid contamination.
• Evapourate off the water, leaving the salt.
Making insoluble salts (precipitation reaction)
Precipitates/Insoluble salts:
• Lead chloride PbCl2
• Lead sulphate Pb SO4
• Silver chloride AgCl
Lead salt + Metal chloride -> Lead chloride + Insoluble salt
Method:
• Mix two solutions that contain the required ions. e.g.
Lead nitrate + Sodium chloride -> Lead chloride (ppt) + Salt
Pb(NO3)2 (aq) + 2NaCl (aq) -> PbCl2 (s) + 2NaNO3 (aq)
• This is also used in water purification for removing poisonous metal ions (e.g. Pb), or removing metal ions that can cause hardness in the water (e.g. Ca2+, Mg2+)
Electrolysis
The use of electricity to split up a dissolved/molten ionic compound into its elements.
Electrolyte
A liquid used in electrolysis to conduct electricity.
Anode
The positive electrode.
Cathode
The negative electrode.
Anion
A negative ion (attracted to positive, anode electrode)
Cation
A positive ion (attracted to negative, cathode electrode)
Electrolysis: Oxidation
Electrons are lost.
O xidation
I s
L oss
Symbol is (O)
e.g. 2Br- - 2e- -> Br2 (g)
Electrolysis: Reduction
Electrons are gained.
R eduction
I s
G ain
Symbol is (H)
e.g. Pb2+ + 2e- -> Pb (s)
What is another name for sodium chloride solution (NaCl (aq))?
Brine
Why is the electrolysis of brine/sodium chloride solution important industrially?
- Chloride: bleach, plastics
- Sodium hydroxide (alkali): used in chemical industry e.g. soaps, cleaning products
- Hydrogen: used in the Haber process
How do you prove that hydrogen gas is present?
The pop test
The Electrolysis of Lead bromide
(See diagram) • Br- ions are attracted to the anode. Bromine gas is formed 2Br- -2e- -> Br2 (g) Oxidation as electrons are lost.
• Pb2+ ions are attracted to the cathode.
Lead metal is formed.
Pb2+ + 2e- -> Pb (s)
Reduction as electrons are gained.
The Electrolysis of Sodium Chloride solution/brine?
(See diagram) • Cl- ions are attracted to the anode. Chlorine gas is formed 2Cl- -2e- -> Cl2 (g) Oxidation as electrons are lost.
• H+ ions are attracted to the cathode.
Hydrogen gas is formed.
2H+ + 2e- -> H2 (g)
Reduction as electrons are gained.
- Sodium hydroxide (Na+OH-) solution is left behind.
- The hydrogen comes from the H20 in the brine. The H= ion is attracted to the cathode, and leaves the OH- to react with the Na.
The Electrolysis of Aliminium oxide
(See diagram) • O2- ions are attracted to the anode. Oxygen gas is formed 2O2- - -4e- -> O2 (g) Oxidation as electrons are lost.
• Al3+ ions are attracted to the cathode.
Aliminium metal is formed.
Al3+ + 3e- -> Al (s)
Reduction as electrons are gained.
The Electrolysis of Al2O3/bauxite
(See diagram)
Al2O3 is bauxite. It has a mpt of 2000 degrees Celsius.
• Cryolite (a rare, different aliminium ore) is used to lower the mpt to 900 degrees Celsius. This makes it cheaper, and reduces the amount of resources required, so less CO2 produced.
• 02- ions are attracted to the anode (Carbon: graphite).
Oxygen (actually CO2) gas is formed
2O2- -4e- -> 02 (g)
Oxidation as electrons are lost.
• Al3+ ions are attracted to the cathode.
Molten aliminium metal is formed.
Al3+ + 3e- -> Al (s)
Reduction as electrons are gained.
- The molten aliminium is let out through a valve.
- The anode has to be replaced regularly as it is carbon (graphite),a nd reacts with the oxygen to form CO2.
- You use graphite instead of another metal as it not only conducts electricity, but is also fairly unreactive.
Electroplating
(See diagram) When you coat the surface of one metal with another metal. You would do this either for decoration, or to increase the objects conductivity.
• The object to be plated is always attatched to the negative electrode as metal ions are always positive. This means they will be attracted to the cathode.
Electroplating using silver
The anode is a rod of pure silver. The electrolyte is silver nitrate solution (Ag+NO- 3)
• The Ag+ ions are attracted to the cathode.
They coat the object.
• The silver ions come from the solution. But the pure silver anode acts as a “top up”/source of extra ions if they’re all used up.
