[jjkwest1]

Estimate the heat released when ethene reacts with Hbr to give CH3CH2Br. Bond enthalpies are C-H: 412 kj/mol, C-C: 348 kJ/mol, C=C: 612 kj/mol, C-Br: 276 kJ/mol, Br-Br: 193 kJ/mol, H-Br: 366 kJ/mol

Can anyone tell me if i did this correct?

C2H4 + HBr -----> CH3CH2Br

Heat released= bonds broken - bonds formed

(612+4(412)+366)-(5(412)+276+348) = -58 kJ/mol

[UG]

Looks good.

[lancenti]

A faster way to do it would be to note that the only two bonds you break are the C=C and H-Br and replace it with two C-Br, two C-H and a C-C bond. It saves a few seconds when you're in a rush, and the less keys you press the less likely you're going to make a mistake. You notice that the 4 C-H bonds you break then form back simply cancel each other out.

Of course, in real life, the C-H bond in ethene is different from the C-H bond in 1,2-dibromoethane but since your data doesn't provide for that difference, there's no need.