## methods

aaronharouni
Posts: 72
Joined: Fri Sep 28, 2018 12:15 am

### methods

How do you know which method to use when dealing with bond enthalpies?

whitney_2C
Posts: 74
Joined: Fri Sep 28, 2018 12:28 am

### Re: methods

If you're dealing with bond enthalpies then you use the equation: $\Delta Hrxn = \sum H (bonds broken)-\sum H(bonds formed)$

Eruchi Okpara 2E
Posts: 53
Joined: Fri Sep 28, 2018 12:28 am

### Re: methods

How do you know which bonds need to be broken?

Ethan Yi 1K
Posts: 62
Joined: Fri Sep 28, 2018 12:28 am

### Re: methods

aaronharouni wrote:How do you know which method to use when dealing with bond enthalpies?

draw the lewis structures

eden tefera 2B
Posts: 39
Joined: Fri Sep 28, 2018 12:21 am

### Re: methods

You can also cross out bonds if both the products and reactants both have the same number!

AnnaYan_1l
Posts: 96
Joined: Fri Apr 06, 2018 11:05 am
Been upvoted: 1 time

### Re: methods

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!

Cynthia Ulloa
Posts: 52
Joined: Fri Feb 23, 2018 3:02 am

### Re: methods

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

Hannah Yates 1K
Posts: 59
Joined: Fri Sep 28, 2018 12:27 am

### Re: methods

If you are given (or took to look up) the bond enthalpies, you then just have to use the equation that someone put above.

Cameron_Greenberg_3C
Posts: 60
Joined: Fri Sep 28, 2018 12:26 am

### Re: methods

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

Return to “Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)”

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