the amount of ice B1. A The standard molar enthalpt of fomination of dihor the c

Question

the amount of ice B1. A The standard molar enthalpt of fomination of dihor the compound he becauxe cannot be prerared by the fea cricen of changus, can be cakulalel from other anges can be how The follow enilialpy Ever 2032.9 kymal la) Show how these equaations can be added together to e equation for the formacion BiH.lg from Bs) and H in their standard states. Assign alry changes to each h) Calculate A Ho for R2H. Draw an energy diagram that shows how the various enthalpies in this problem fd) s the formation B2Helg) from its elements exo- or endochermic? 82. Chloromethane, CH a compound found throughoneu

Explanation / Answer

a)

formation of B2H6 from B(s) and H2(g)

so...

2B(s) + 3H2(g) --> B2H6(g)

we need B(s) in the left side, use the RXN1 and divide by 2,

We need H2 in the left side, with 3 cofficient, so multiply RXN2 by 3

finally, B2H6 must go to the right, invert this

so

2B(s) + 3/2O2(g) = B2O3 HRxn = -2543.8/2 = -1271.9 kJ

3H2 + 3/2O2 = 3H2O HRxn = (-241.8)*3 = -725.4 kJ

B2O3 + 3H2O --> 3O2 + B2H6 HRxn = -(-2032.9) = 2032.9 kJ

add all

2B(s) + 3/2O2(g) 3H2O + 3H2 + 3/2O2 + B2O3= B2O3 + 3H2O +3O2 + B2H6   

cancel common terms

2B(s) + 3H2(g) = B2H6 (s) Htotla = -1271.9 - 725.4 + 2032.9 =35.6 kJ/mol

HRxn = 35.6 kJ/mol

b)

dH for H2H6, as given before is 35.6 kJ/mol

c)

the energy diagram is essneitally as follows:

- negative species will go on the bottoms

- species near 0, go in the half point

- species with possitive values go on the top

d)

this is possitive in dHrxn sign, therfore, the enthlpy of products > enthalpy of reactants, this absorbed heat, meaning it is ENDOTHERMIC

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