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### methods

Posted: Sat Feb 09, 2019 1:34 pm
How do you know which method to use when dealing with bond enthalpies?

### Re: methods

Posted: Sat Feb 09, 2019 2:08 pm
If you're dealing with bond enthalpies then you use the equation: $\Delta Hrxn = \sum H (bonds broken)-\sum H(bonds formed)$

### Re: methods

Posted: Sat Feb 09, 2019 11:00 pm
How do you know which bonds need to be broken?

### Re: methods

Posted: Sat Feb 09, 2019 11:00 pm
aaronharouni wrote:How do you know which method to use when dealing with bond enthalpies?

draw the lewis structures

### Re: methods

Posted: Sun Feb 10, 2019 12:50 pm
You can also cross out bonds if both the products and reactants both have the same number!

### Re: methods

Posted: Sun Feb 10, 2019 12:51 pm
eden tefera 2B wrote:You can also cross out bonds if both the products and reactants both have the same number!

Would you be able to explain what you mean with an example? This seems like a helpful tip, but I'm not sure how to do this in practice. Thank you!

### Re: methods

Posted: Sun Feb 10, 2019 1:10 pm
Eruchi Okpara 2E wrote:How do you know which bonds need to be broken?

if you draw out the lewis structures you will be able to cross out any new bonds formed or any bonds that were broken. This method will make it easier to go about these problems involving bond enthalpies

### Re: methods

Posted: Sun Feb 10, 2019 4:18 pm
If you are given (or took to look up) the bond enthalpies, you then just have to use the equation that someone put above.

### Re: methods

Posted: Sat Feb 16, 2019 9:11 pm
There are three main methods.
1. Standard Enthalpy of Formation, given by the enthalpy of formation of each reactant and product
2. Hess's Law, given by several equations that need to be manipulated to add up to the given equation
3. Bond Enthalpy, given by the enthalpies of each bond in the reactant and product molecules