1. The problem statement, all variables and given/known data This is a single displacement reaction aluminum + hydrochloric acid --> 2. Relevant equations 3. The attempt at a solution Since I know its single displacement, and I know that aluminum can't trade places with chlorine because one is a metal and one is a non-metal, aluminum must trade places with hydrogen, which I know can trade places with a metal. Al + HCl --> H + AlCl Since I know that hydrogen is a diatomic element, I must change it to H2 Al + HCl --> H2 + AlCl Now it's out of balance because there are 2 hydrogens on the right. So I balance it by multiplying the left HCl by 2. Al + 2HCl --> H2 + AlCl This leaves Cl out of balance, so I multiply the right one by 2. Al + 2HCl --> H2 + 2AlCl This leaves Al out of balance, so I multiply the left one by 2. 2Al + 2HCl --> H2 + 2AlCl Seems to be balanced now. But when I look up the answer by Googling, I find that I should have ended up with 2Al + 6HCl --> 2AlCl3 + 3H2 Where did I go wrong? Thanks!