Chemical Reactions, Energetics, Electrolysis Flashcards
What is an endothermic & exothermic reactions?
An exothermic reaction gives energy to the surroundings from the reaction so energy forming new bonds is greater than that breaking existing bonds.
An endothermic reaction takes energy from the surroundings to the reaction so energy breaking bonds is greater than forming new bonds.
What is activation energy, energy change and bond energies?
Activation Energy is the minimum energy needed to start a reaction.
Energy Change is the different in energy between reactants and products (- is exothermic + is endothermic).
Bond Energies is the energy need to break 1 mol of a particular bond (Kj/mol).
What are acids, alkalis and bases?
What is concentration and strength of acids?
An acid is a substance that releases H+ ions when dissolved in water.
An alkali is a substance that release OH- ions when dissolved in water.
A base is a substance that neutralises acids by producing a salt and a water
The concentration is the number of particles in a given volume that are acid.
The strength of an acid is the measure of how much an acid is ionised.
What are the different acid reactions?
Acid + Base —> Salt + Water (Neutralisation)
Acid + Carbonate —> Salt + Water + Carbon Dioxide
Acid + Metal —> Salt + Hydrogen
Acid + Metal hydroxide —> Salt + Water
What are redox reactions?
Oxidation is the gain of oxygen and the loss of electrons.
Reduction is the loss of oxygen and the gain of electrons.
A redox reaction is where both oxidation and reduction happen at the same time.
In a redox reaction both happen where an oxidising agent oxidises the other and a reducing agent reduces the other.
What is electrolysis? Electrolyte? Electrode?
Electrolysis is the splitting up of ionic compounds into separate elements using electrodes as a result of their conductivity when molten.
An electrolyte is a compound in a solution which contains mobile ions to conduct.
An electrode are two rods made from an inert metal or graphite; the negative is cathode and the positive anode.
What are the rules for the products of aqueous electrolysis?
At the cathode, the least reactive is produced which is usually hydrogen.
At the anode, a halogen is produced, otherwise hydroxide is produced but oxygen is observed.
Gold, silver, copper and platinum are exceptions.
What is electroplatting?
Electroplatting is a type of electrolysis that uses non-inert electrolytes which change during electrolysis.
Cathode is the object to be coated; anode is the metal used to coat; electrolyte is a solution of metal ions.
At the cathode, the metal ions are reduced; at the anode, the metal ions are oxidised.
How do you purify copper?
Purifying copper involves the obtaining of copper through electrolysis where the anode is impure copper and the cathode is pure copper. Impurities then fall of the impure copper and stable copper atoms are attracted to the cathode: pure copper.
What are bond energies?
The energy needed to break 1 mol of a particular bond is the bond energy. It is measured in kilojoules per mole.
How to calculate the energy change using bond energies?
Energy change = Energy transferred to break bonds - Energy transferred when bonds made
