IB Chemistry Topic 5 Energetics 5.2 Hess's Law with enthalpy of formation and enthalpy of combustion

IB Chemistry Topic 5 Energetics 5.2 Hess's Law with enthalpy of formation and enthalpy of combustion
How to use Hess' Law to work out enthalpy problems. The most valuable think to learn is how to work out if the formula is products less reactants or reactants less products. Practice problems for Hess Law, enthalpy of formation and enthalpy of combustion

0:12 Hess's law definition
0:52 Hess's law reaction diagram
1:15 Hess's law example problem
1:46 Enthalpy of formation definition
2:50 Enthalpy of formation example problem 1
4:22 Enthalpy of formation example problem 2
5:43 Enthalpy of combstion definition
6:19 Enthalpy of combustion example problem
7:22 Summary of formula

5.2 Hess's Law SL
• The enthalpy change for a reaction that is carried out in a series of steps is equal to the sum of the enthalpy changes for the individual steps.
• Application of Hess’s Law to calculate enthalpy changes.
• Calculation of ∆𝐻 reactions using ∆Hf° data.
• Determination of the enthalpy change of a reaction that is the sum of multiple reactions with known enthalpy changes.

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[zosiamatuszczyk]

There is a small mistake 4:22 - the final result should be 65 kJ/mol.

[poojithapai]

Hello Mr Weng,
Where exactly did you get the values for the enthalpy of formation for calcium carbonate and calcium chloride and all that in problem number 1. I couldn't find any in the data booklet :(

[TravisHeadsFather]

problem 2, the answer should be - 511.5 KJ, exothermic reaction? or does it not matter... (And also for other people getting close to the same number he gets it is probably because you have different values for the formation of the compounds (as well as him using rounded values for e.g. number of moles), I got - 553 KJ using the most recent data in the data booklet at the time, 3rd edition first assessment 2016.

[MoFootballForU]

Mr.Weng I still don't understand how you calculated the formulas by just looking at the questions. Could you explain it in another way or written form? Thank you.

[josh]

So you use enthalpy of combustion, when measuring enthalpy of formation?

[GummyBear]

I don't get why for 5:33 you multiple it when you're suppose to divide.