All matter is composed of particles. This is known as the particle theory and it is best to familiarize yourself with this theory now. Click to go to particle theory. Cooking involves chemical reactions. During chemical reactions collisions take place between substances that ultimately result in the formation of new products. In the kitchen we use a number of ways to get chemical reactions happening quickly .

The first is to dissolve the substances we wish to react together. Particles forming a solid do not move about but simply remain in a fixed position. The likely chance that they will collide with particles of another solid substance is very remote. When solids dissolve in water their particles become free to move about and interact with other particles. A chemical reaction is more likely to occur when substances are dissolved.

The animation above shows the particles of two solid substances. As water is added these particles become mobile able to interact and collide with each other causing a chemical reaction.

A perfect example of this is the fizzy drink Eno. Eno contains an acid(citric acid) and sodium bicarbonate. Normally these two substances react vigorously to produce carbon dioxide gas resulting in a fizzy drink. When in a powder form, however, no reaction takes place.

With reference to the collision theory and particle theory of matter explain why no reaction takes place when the citric acid and sodium bicarbonate are mixed in the solid state.

When water is added the results are spectacular. Water frees the citric acid and bicarbonate particles and allows the chemical reaction to proceed. The production of gas is clearly visible.