<p>This is a question in PR and I suspect that the answer is wrong. </p>
<p>calculate approximate (delta)H (enthalpy) for CH4+Cl2-----CH3Cl+HCl given the following bond energy
C-H bond=410kj/mol
Cl-Cl bond= 330kj/mol
Cl-Cl bond=240kj/mol
H-Cl bond=430kj/mol</p>
<p>Is (delta)H= H after-H before? Then is the answer +110kj which means that it is an endothermic reaction?</p>
<p>A reaction’s enthalpy can be approximated through summation of bond energies (find total heat lost and gained, subtract and divide to get one mole)</p>
<p>and generally a positive delta H is endothermic</p>
<p>So the answer is +110kj NOT -110kj?</p>
<p>Think of it in terms of bonds broken minus bonds formed.</p>
<p>Left minus right</p>
<p>We can’t help you figure out the answer because you listed Cl-Cl twice…Sorry!</p>
<p>oooops.
It should be
C-Cl bond =330kj/mol
Cl-Cl bond = 240kj/mol</p>
<p>+210 kJ</p>
<p>endothermic</p>
<p>um if nicksyn is correct then the answer would be -110kj and the reaction would be exothermic. However he isn’t. They are not asking for Bond energies. When solving for delta h, it is the sum of the products minus the sum of the reactions. In this case:
sum of products = 1990
sum of reactants = 1880.
so the answer is 110 kj and it is endothermic.</p>
<p>Shouldn’t bond energy be positive as well since enthalpy increases?</p>
<p>I got -110. Bonds Broken-Bonds formed. Is that the answer the book says? But then again that’s bond energies which isn’t what this is asking…
Just my .02 but I would go with the book unless it’s one of those crappy ones you get when the others are sold out.</p>
<p>OK I got it!!
The numbers refer to the bond energy but the energy will be released when bonds are formed.</p>
<p>it’s reactants - products</p>
<p>source: chemistry genius</p>