Writing a balanced chemical equation

Question

I always struggle writing a chemical equation from a worded problem so any tips on learning it? (not taking balancing into account) More specifically, I never know which reactants will pair with each other to form the products along with any subscript changes.

Answer 1

Step 1: Just write down the compounds as best you can - ionic bonded compounds will give you metal/non-metal or metal and polyatomic ion pairs or molecular bonded compounds with the appropriate subscripts to match the wording (Example: Dinitrogen pentoxide = N₂O₅ because "di" is the prefix for 2 and "pent" is the prefix for 5). Make sure diatomic gases are shown correctly (H₂, O₂, Br₂, F₂, I₂, N₂, Cl₂)

Step 2: Balance the ionic charges with appropriate subscripts (Example: Calcium hydroxide = Ca(OH)₂ because Ca is +2 and Hydroxide (OH) is -1 so it takes 2 hydroxides to balance the + 2 charge)

Step 3: Balance the number of atoms of each element on one side of the equation with the other side of the equation using by changing coefficients.

1. Start with any metal that is only listed in once on one side of the equation, adding a coefficient to the compound so the number of atoms match the other side.
2. Repeat, saving elements that are listed in multiple compounds until the end.
3. If you have only the possibility of having an even number of atoms on one side (O₂, for example), and you end up with an odd number on the other side, double the odd number and rebalance.

Step 4: Double check the numbers of all atoms to make sure you got it right (each side need the same number).

It sounds like one of the issues you have is replacement reactions. To see if a single replacement reaction occurs you need to use an Activity Series list that shows which of the elements is most reactive. To see if a double replacement reaction occurs, you need to use a solubility table to look for precipitates (if one is formed that reaction occurs otherwise the elemental ions will remain in the aqueous solution unreacted). If you don't have either of those lists/tables, ask your teacher or look in your book or online.