C3 - Chemical Reactions
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What is the conservation of mass?
During a chemical reaction, no atoms are destroyed and no atoms are created.
What is Avogadro’s constant?
The number of atoms or molecules in one mole of a substance, equal to 6.022 x 10 23.
What is a limiting reactant?
The reactant that is completely used up in a reaction.
The formula which links mass, molar mass and moles?
Mass = moles x Mr
Define an exothermic reaction
An exothermic reaction is one which gives out energy to the surroundings, usually in the form of heat, and usually shown by a rise in temperature of the surroundings.
Define an endothermic reaction
An endothermic reaction is one which takes in energy from the surroundings, usually in the form of heat, and usually shown by a fall in temperature of the surroundings.
Define an exothermic reaction in terms of bonds
More energy is released in making bonds than is taken in when breaking bonds
Define an endothermic reaction in terms of bonds
More energy is taken in to break bonds than is released to make bonds
Define activation energy
The minimum amount of energy needed for bonds to break and a reaction to start
What is an oxidation reaction?
A loss of electrons in a reaction is called oxidation
What is a reduction reaction?
A gain of electrons in a reaction is called reduction
Describe a neutralisation reaction
The reaction between acids and bases is called neutralisation. It produces a salt and water. When an acid neutralises a base, or vice versa, the products are neutral
Fill in the gaps: Acid + Metal –> ……….. + ………..
Acid + Metal –> Salt + Hydrogen
Fill in the gaps: Acid + Metal Carbnonate –> …….. + …….. + …………
Acid + Metal Carbonate –> Salt + Water + Carbon Dioxide
Fill in the gaps: Acid + Alkali –> …… + ……..
Acid + Alkali –> Salt + Water
Explain the term dilute acid
An acid with a low proportion of acid molecules in a set volume of water
Explain the term concentrated acid
An acid with a high proportion of acid molecules in a set volume of water
Explain the term strong acid
Strong acids ionise almost completely in water. A large proportion of acid molecules dissociate to release H+ Ions
Explain the term weak acid
Weak acids do not fully ionise in water. Only a small proportion of acid molecules dissociate to release H+ Ions
How does concentration affect pH?
If the concentration of H+ increases by a factor of 10, the pH decreases by 1.
What is formed at the cathode?
Metals
What is formed at the anode?
Non-metals
What happens at the cathode during the electrolysis of aqueous solutions?
At the cathode, if hydrogen ions and metal ions are present, hydrogen gas will be produced if the metal is more reactive than hydrogen (e.g. sodium). If the metal is less reactive than hydrogen (e.g. copper or silver), then a solid layer of the pure metal will be produced instead.
What happens at the anode during the electrolysis of aqueous solutions?
At the anode, if halide ions (Cl-, Br-, I-) are present, molecules of chlorine, bromine and iodine will be formed. If no halide ions are present, then oxygen will be formed from the hydroxide ions.