Why do the raisins pop in baking soda and vinegar?

The chemical reaction between baking soda (sodium bicarbonate) and vinegar (acetic acid) produces carbon dioxide gas. The gas forms bubbles that cause the raisins to rise to the surface. When the bubbles burst, the raisins pop.

The chemical equation for the reaction is:

NaHCO3 + CH3COOH → CO2 + H2O + NaCH3COO

The carbon dioxide gas is what causes the raisins to pop. The reaction also produces water and sodium acetate, but these do not have a significant effect on the raisins.