Question

Diboron trioxide is used to make borosilicate gl ass that resists breaking when exposed to extremes in temperature He Calculate AH for the reaction: (12 pts.) 4 B(s)+3 02(g) 2 B2O3(s) from the data below: AH -2035 kJ B203(s)3 Hz0(g) B2H(g) +3 O2(g) 1. +36 kJ AH B2H(g) 2 B(s)+ 3 H2(g) 2. Cd Th AH=-484 kJ 2 H2(g)+ O2(g) Oin 2 H2O(g) 3. At Ra A Bg Mc LyTO MDs Re Ca Nh Eu Gd Tb Dy Ho ErTmY Nd P Cs Fim Md No Ci BlC olie Is the reaction exothermic or endothermic? (2 pts.) b.

Answer 1

double the first equation

2B2H6_(g) + 6O2_(g) --------> 2B2O3_(s) + 6H2O_(g) $\Delta$H = - 4070 KJ

double the second equation

4B_(s) + 6H2_(g) ----------> 2B2H6_(g) $\Delta$H = 72 KJ

reverse and triple the third equation

6H2O_(g) ----------> 6H2_(g) + 3O2_(g) $\Delta$H = 1452 KJ

add all 3 equations

2B2H6_(g) + 6O2_(g) --------> 2B2O3_(s) + 6H2O_(g) $\Delta$H = - 4070 KJ

4B_(s) + 6H2_(g) ----------> 2B2H6_(g) $\Delta$H = 72 KJ

6H2O_(g) ----------> 6H2_(g) + 3O2_(g) $\Delta$H = 1452 KJ

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4B_(s) + 3O2_(g) -----------> 2B2O3_(s) $\Delta$H = - 2546 KJ

b) as $\Delta$H = negative reaction is exothermic