Ch21 - Chemical reactions

• Physical change - a change that does not result in any substance forming. It is only the appearance of the substance that changes. Can usually be reversed.

  Chemical change (chemical reaction) - a change that does result in a new substance forming. Can be seen by a change of colour or bubbles. Can be difficult to reverse.

  Reactants - the chemicals reacting together in the reaction.

  Products - the chemicals produced in the reaction.

  Law of conservation of mass - when a reaction occurs, the mass of the products must equal to the mass of the reactants.
• Investigating law of conservation of mass:

  1. Ice cube experiment - physical change
  2. Alka-seltzer tablet in a balloon - chemical change

  Physical change:

  • Place ice cubes in a container and seal it. Measure its mass on a scale. Allow for the ice cubes to melt into water. Measure the mass - it must equal the ice cube mass.

  Chemical change:

  • Place an alka-seltzer tablet in a balloon and secure the balloon on a conical flask with water. Measure the mass and tip the balloon over, the balloon should inflate, proving a reaction occurred. Measure the mass of the apparatus, it must equal.