To 2 mL of tap water in a test tube, add 10 drops, one at a time, of 12 M hydrochloric acid, HCl. Use a thermometer to check for any temperature change. Save the diluted acid for future use in Step 5. Rinse the eye-dropper thoroughly. What do the reactants look like?
What happened when the HCl was added to the H2O? Make observations concerning anything that might indicate a chemical reaction, such as production of a gas or a precipitate, color change or temperature change (did the test tube get cold or hot?).
Why do you think a reaction has, or has not, taken place?
Whenever the temperature changes as the result of chemicals being added together, the enthalpy of the products will differ from the enthalpy of the reactants.
Has a temperature change taken place?
Has an energy change taken place?
In order to get the solution back to the original temperature for an energy comparison with the reactants, will you need to heat or cool the test tube?
Did this reaction release energy or take on added energy?
Therefore, is the enthalpy of the products greater or less than the enthalpy of the reactants?
Symbol Model: HCl + H2O → H3O+(aq) + Cl-(aq) + heat
Energy Model: Reactant's Enthalpy (E1) → Product's Enthalpy (E2) + heat