IS steel a pure stubstance or a mixture

When will le chatelier's principle come into effect? at the beginning of a reaction, when there are only reactants when a reaction has reached chemical equilibrium when a catalyst is added to a reaction mixture when a reaction is occurring but not yet at equilibrium

If two objects at different te,peraure are in contact with each other what happens to their temperature

Which rate indicates the number of children that would be born per woman if she were to live to the end of her child bearing years