Shazia has built a campfire and it is burning well. Robert collects some damp logs and puts them on the fire. Shazia is annoyed with Robert because the fire now burns more slowly. There has been a change in the rate of reaction.
Ok, I got the camfire going. Could you bring some more logs?
Ok, I found these.
Were the logs damp?!
The water in the logs absorbs heat and evaporates and that means that more heat needs to be applied in order to rise the temperature.
And because it uses the heat, it slows the fire.
Oh, kind of like how sweating cools us down?
Yes, exactly. Now go get more logs unless you plan on freezing tonight.