2.2 Conservation of Mass in Chemical Equations
chemistry
Balancing Chemical Equations
Because of the Law of Conservation of Mass, we can count atoms and use math to balance the number of atoms in chemical equations.
- Word equation:Methane + oxygen--> water + carbon dioxide
- Skeleton equation: CH4(g) + O2 (g)--> H2O(l) + CO2(g)
- To balance the compounds, take note of how many atoms of each element occur on each side of the reaction arrow:
1 Carbon, 4 Hydrogen, 2 Oxygen --> 1 Carbon, 2 Hydrogen, 3 Oxygen
- To balance, attempt to find values that equate atoms on both sides
1 Carbon, 4 Hydrogen, (2x2) Oxygen --> 1 Carbon, (2x2) Hydrogen, (2x1)+2 Oxygen
- Balanced equation: CH4(g) + 2O2 (g) --> 2H2O(l) + CO2(g)
Balance chemical equations by following these steps:
- Trial and error will work, but can be very inefficient
- Balance compounds first, elements last
- Balance one compound at a time
- Only add coefficients; NEVER change subscripts!
- If H and O appear in more than one place, attempt to balance them LAST
- Polyatomic ions (such as SO42–) can often be balanced as a whole group
- Always double-check after you think you are finished!
Balance the following:
Fe + Br2 --> FeBr3
Sn(NO2)4 + K3PO4 --> KNO2 + Sn3(PO4)4
C2H6 + O2 --> CO2 + H2O