2. Address each of the following: a. Write a balanced equation for the formation

Question

2. Address each of the following: a. Write a balanced equation for the formation of one mole of NaCl(s) from its elements. The enthalpy change for this reaction is =-411.1 kJ/mol. b. Write a balanced equation for the formation of one mole of NaCI(aq) from its elements. The enthalpy change for this reaction is "f-407.3 kJ/mol. c. Write a balanced equation for the conversion of solid NacI(s) to aqueous NaCl(aq). d. Using Hess's Law, and the previous three equations, calculate Hoon, in kJ/mol, when NaCl(s) dissolves in water. Is this process highly or slightly exothermic or endothermic?

Explanation / Answer

a)

12 mol fo NACl

must be formed from Na(s) and Cl2(g)

then

Na(s) + 1/2Cl2(g) --> NaCl(s)) H1 = -411.1

b.

for 1 mol of NACl....

Na(s) + 1/2Cl(aq) --> NaCl(aq) H2 = -407.3

note that phase changes!

c and d

balance equation

NaCl(s) --> NaCl(aq)

for HRxn

Na(s) + 1/2Cl2(g) --> NaCl(s) H1 = -411.1

Na(s) + 1/2Cl(aq) --> NaCl(aq) H2 = -407.3

revert H1

Na(s) + 1/2Cl(aq) --> NaCl(aq) H2 = -407.3

NaCl(s) --> Na(s) + 1/2Cl2(g) H1 = -1(411.1) = 411.1

Htotal =-407.3 + 411.1

Htotal = 3.8 kJ/mol

since it is positive, the reaciton must be endothermic

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