Question

1. Write net ionic equations for: a. the reaction between hydrochloric and sodium hydroxide b. the reaction between calcium and water ( assume that the solution containing the calcium hydroxide is dilute and that the calcium hydroxide has completely dissociated into its ions) c. the reaction between calcium and hydrochloric acid. 2. a.Arrange the equations in 1a and 1b so that algebraic addition yields the equation in 1c. b. Add your experimentally determined values for the molar heats of reaction as indicated by the equations above. the summation is the theoretical heat of reaction for calcium and hydrochloric acid. 3. Compare the heat of reaction for calcium and acid that you calculated in 2b above with the value you determined experimentally and discuss possible reasons for any discrepancy. (e.g. What kinds of experimental errors might have affected your results? Did you make any observations that might suggest that Hess's law should not be used for this set of reactions ? Did you make any assumptions that you believe to be suspect?) What can you conclude about the validity of Hess's law from your experiments ?

Answer 1

a.

H⁺ + HO^- = H₂O                              dH1=….. (experimental value)

b.

Ca + 2H₂O = Ca²⁺ + 2HO^- + H₂         dH2= … ( exprimental value)

c.

Ca + 2H⁺ = Ca²⁺ + H₂ dH= ......(experimental value)

2.a.

2H⁺ + 2HO^- = 2H₂O

Ca + 2H₂O = Ca²⁺ + 2HO^- + H₂

……………………………………(sum)

Ca + 2H⁺ = Ca²⁺ + H₂

2.b.      

dH (calculated value) = 2xdH1 + dH2

If dH (calculated value) has not the same value as dH(experimental), you had some experimental errors   ( how exact was your calorimetric mesurements?). Hess law remains valid.