Chemistry Unit 1 Question Edexcel

What is the difference between bond enthlapy and mean bond enthlapy ?

Thanks, one more question.

When you have an enthlapy change, say exothermic, the enthlapy change is neagtive (on a enthlapy level diagram, the products are of a lower enthlapy and so is neagtive) and is this due to some of the enthlapy being used to create the heat (i.e. exotehrmic) and thus the enthlapy in the system is reduced and so is lower ?

E N T H A L P Y

Check out this link on enthalpy ...

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So some of the enthalpy is transformed to heat and thus lower enthalpy

Yes, you can think of enthalpy as that portion of the internal energy which can be transformed into heat energy (or vice versa)

Thanks, can you help me with this question please


Formula of substance Standard enthalpy of formation/kJ mol–1
CH4(g) –75
O2(g) 0
CO2(g) –394
H2O(g) –242

The equation for the complete combustion of methane at 150 °C is:
CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
Use the given data to calculate the enthalpy of combustion of methane under these conditions.

I suggest you go through this mini-tutorial on Hess' law, which covers this kind of problem along with other Hess's law calculations:

Hi, there is a calculation error on the 2nd final slide in the example page. It says that -1697 + 1560 = -147 Kjmol when it should be -137 Kjmol