Can some one explain balacing chemical equations to me

[eeeeee]

I don't understand how to balance equations. I have a huge test in science and i don't understand how do balance them. she says there is a easy short cut but she dosent want to to teach us it beacouse she thinks it will be to easy. could some one tell me a easy way or just explain how to do this.

here are a few examples

Na +I2 (arrow going right) NaI


N2 + O2 (arrow going right) N2O

 

[ksinclair13]

$$Na + I_2 \longrightarrow NaI$$

Now, if you have 2 I on the left side, you will need the same on the right side. So, if you place a 2 in front of the NaI, the I's are balanced, but now you have to go back to the left side to balance the Na's. What number should you place there?

$$?Na + I_2 \longrightarrow 2NaI$$

Try to follow this logic for the second one and see what you can come up with :).