LAB ACTIVITY Pre-Lab Questions al 1 Consider the following three reactions React

Question

LAB ACTIVITY Pre-Lab Questions al 1 Consider the following three reactions Reaction 5 Reaction 6 Reaction 7 NaOH(s) NaOH(aq) NaOH(s) + HCl(aq) NaCl(aq) +HjO (f) NaOH(aq) + HCl (aq) NaCI(aq) +H,0 (r) Show how you can use Reactions 5 and 6 to describe Reaction 7. What Hess law say about the change in enthalpy of reactions? 3 How could you support Hess'law using the heats of reaction in question 1 In the space provided on pages 149-150 of the data sheet, design a lab procedure that uses the calorimetry materials and the procedure from Lab Activity 5.1 to collect data to support Hess' law This m he the first time you have designed a procedure from the beginning When scientists develop

Explanation / Answer

(1)

When reaction 5 is reversed and is then added to reaction 6, we obtain reaction 7.

Thus, mathematically, the relation between these two reactions can be expressed as:

(7) = (6) - (5)

(2)

.According to Hess' law, if a reaction can be expressed as a combination of two smaller reactions, then its ethalpy change can also be expressed by a similar combination of enthalpies of the smaller reactions.

(3)

.In this case, Hess' law holds as shown below:

Assume that enthaply change for the reactions (5), (6) and (7) are dH5, dH6 and dH7 respectively.

According to Hess' law, we have the following relation:

dH7 = dH6 - dH5

Hope this helps !

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