Unit 4 Lesson 2

Making Predictions

Observing Change

When a substance changes phase or dissolves, its chemical formula does not change.

When you look at a chemical equation, it can tell you the different kinds of changes going on like changes in phase or identity of the substance.

Ex: CaCl2(aq)+ 2NaOH(aq) ---> Ca(OH)(s) + 2NaCl(aq)

For this chemical equation you start of with two aqueous reactants, but when they undergo the reaction you can tell that there was a change visually because now one of the products is a solid that you would be able to see. The equation would also allow you to see which substances broke up and rearranged to combine into a solid. You wouldn't be able to know this without seeing the chemical equation.

Some things a chemical equation alone can't tell you is if there were any changes in temperature or color after or during the reaction or how quickly it happened.

Practice Problems

4) a. NaCl(s) ---> NaCl(aq) b. MgS(s) ---> Mg(s) + S(g) c. Ti(s) + O2(g) ---> TiO2(g)

5) a. Two aqueous solutions combining leaving behind water and emitting chloramine gas and aqueous sodium hydroxide b. two aqueous solutions combining to produce hydrazine gas, aqueous sodium chloride, and water

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