8. Thermochemistry
Enthalpy of Formation
Struggling with General Chemistry?
Join thousands of students who trust us to help them ace their exams!Watch the first video
Video duration:
2mRelated Videos
Related Practice
Skip to main content
So at this point, we have identified 3 ways to determine the enthalpy or heat of reaction, otherwise known as delta h of reaction. Here we have constant volume calorimetry, which uses a bomb calorimeter to find the enthalpy of reaction or heat of reaction of combustion reactions. Then we have thermochemical equations which uses stoichiometry and a balanced equation to find delta h of reaction. Then finally Hess's law, if you haven't seen it yet, it uses the enthalpies of partial reactions to find delta h of reaction for the overall reaction. Now if the first three ways are unavailable, then we use the standard enthalpy of formation for substances to find the delta h of reaction. We're gonna say, recall that an element in its standard state is given an enthalpy of formation of 0. So here we can use our standards standard heat of reaction formula to help us find delta h of reaction. Here it's delta h of reaction in its standard state, that's what this little zero means here, equals the summation for the enthalpies of formation of products, minus the summation of the enthalpies of formation for reactants. Or broken down in its simplest way, delta h of reaction equals products minus reactants. So here delta h little circle on top, reaction, this is the standard enthalpy or reaction, heat of reaction in kilojoules. This sigma sign just means the summation or sum up, and we'll see how that works. Here n equals the moles of your substance, and then here, we're gonna say that delta h f with the little circle equals the standard enthalpy or heat of formation for substance in kilojoules over moles, or sometimes joules over moles depending on what units they are. It's always gonna be kilojoules or joules over moles. So now that we've seen this standard heat of form of reaction formula, we're gonna see how it works and use it in the next video. So click on the next video. Let's take a look at an example question.
03:04
