The addition of NH4Cl to a solution of ammonia shows the effect of adding a common ion to a system at equilibrium. Add water to each of two beakers. Add 2 drops of phenolphthalein to each. Add a few ...

Chemical reactions make new chemicals. Atoms are rearranged during a chemical reaction, but the number of atoms does not change. A catalyst is a substance that speeds up a chemical reaction ...

Reversible reactions - AQA Chemical reactions are reversible and may reach a dynamic equilibrium. The position of equilibrium of a reversible reaction can be altered by changing the reaction ...