Source: Pro Teacher
Give each child a sandwich baggie with an ice cube in it. Kids race to melt the ice cube in the bag, transforming their solid into a liquid. Once they have a liquid, the teacher adds a piece of an alka seltzer tablet to their bag - presto: gas (their bag will expand and the contents in their bag will fizz and bubble)! Math - Estimate how long they think it will take them to melt their cube.
Above is a recording sheet for students to use as they are melting their ice cube. Click here to download! Click here for a checklist to assess your students. Also, check out Bag Bomb!