What are three signs that a chemical change has occurred?

In a popular classroom demonstration, solid sodium is added to liquid water and reacts to produce hydrogen gas and aqueous sodium hydroxide. part a write a balanced chemical equation for this reaction. express your answer as a chemical equation. identify all of the phases in your answer.

7. what temperature is need to just dissolve 50 g of nh4cl in 75 g of water? '

What is the independent variable in this investigation? mass volume sample number substance density