Balancing Chemical Reactions
Balanced Chemical Equation Atoms can’t be created or destroyed (All the atoms we start with we must end up with) A balanced equation has the same number of each element on both sides of the equation.
This equation is already balanced What if it isn’t? C + O O C O O C + O 2 CO 2
We need one more oxygen in the products. C + O C O O C + O 2 CO O Can’t change the formula, because it describes what it is (carbon monoxide in this example) CO 2
We need one more oxygen so we make another CO C + O C O O O C But where did the other C come from? C
2 C + O 2 2 CO C + O C O O O C C
1) H 2 + O 2 H 2 O
2) Na + O 2 Na 2 O 2
3) Mg + O 2 MgO
4) N 2 + H 2 NH 3
5) C + S 8 CS 2
6) AgNO 3 + Cu Cu(NO 3 ) 2 + Ag
Rules for balancing: Assemble, write the correct formulas for all the reactants and products Count the number of atoms of each type appearing on both sides Balance the elements one at a time by adding coefficients (the numbers in front) - save H and O until LAST! Check to make sure it is balanced.
Never change a subscript to balance an equation. – H 2 O is a different compound than H 2 O 2 Never put a coefficient in the middle of a formula – 2 NaCl is okay, Na2Cl is not.
Whiteboard Practice
7) Na + O 2 Na 2 O
8) N 2 + O 2 N 2 O 5
9) Cs + N 2 Cs 3 N
10) Al + S 8 Al 2 S 3