How could using either more or less of a chemical in a scientific experiment cause a change in results?

The chemical could have more or less of a reaction to the other chemicals in the experiment

False, as a substance changes from a solid to a liquid and from a liquid to a gas the molecules get farther apart from each other

The population of unionid mussels decreased after zebra mussels were introduced. zebra mussels competed with the unionid mussels for food. the zebra mussels were able to displace the unionid mussels, allowing the zebra mussel population to increase  over the years. the unionid mussel population decreased because  of lack of food.