Stand back It 's going to explode!!!

Today Kohavim lunch bunch friends had the following experiment that Nathaniel brought in from home.
He told us we need the following items: a bottle, a balloon, baking soda, and vinegar.

We had to complete the following steps:

1) First, you pour the baking soda into the balloon using a funnel.
2) Second, you pour a little vinegar into a jar
3) Third, you stretch the balloon over the top of the bottle
4) Fourth, you pull the balloon up over the bottle which will release the baking soda into the vinegar.
5) STAND BACK.

I asked the children what they thought would happen and they said " It's going to explode!!"

It didn't explode but it did inflate. I think it was the great desire to have it explode.. This experiment led to the following question.

Why did they think the balloon inflated?

Was it the baking soda, alone that contributed?
Was it the vinegar alone that contributed?
Was it the combination of BOTH ingredients that made it inflate?

Some thought it was JUST the baking soda, some thought it was JUST the Vinegar, and some thought it was BOTH.

So we proceeded to test out their theories.