Chemistry help

Can someone explain to me state function concept? What do you mean when you say it isn’t related to the paths the reaction takes?

I want to bump this thread to help you get a good reply.
By the way what exam board are you doing ?Is it A level?

Hey! Thank you.
I’m currently studying for AS level exams.

Well so am I, I'm doing OCR B salters. I don't find it difficult at the momnet (I just started about a month ago).

Cool. Good luck amigo
What subjects have you taken up?

-Maths(edexcel)
-Physics (edexcel)
-Chemistry(ocr b)

I'm finding chemistry quite easy atm. Is it me or are A levels actually made up of mainly GCSE subjects?

Can someone explain to me state function concept? What do you mean when you say it isn’t related to the paths the reaction takes?

First hopefully you know what a function is, its just a way of saying that something depends on something else, for example if y=x^2 then you can say that y is a function of x.

equally pV=nRT (the ideal gas equation) can be rearranged to

p=nRT/V then pressure, p, is a function of n, T and V (but not R, because R is a constant)

pV=nRT is called an equation of state, because it described the behaviour of a give state of matter (in this case a gas)

The state of a gas is described by p, V and T.

When we say something (eg enthalpy) is a state function, what we mean is that the value of enthalpy (for example) only depends on the current state of the chemical system you're looking at. It doesn't matter whats happened to the system before, the enthalpy can always be worked out just by looking at the state the system is in now.


One example of this might be thinking about energy.

Imagine two people climbing a mountain, the work they have to do to climb the mountain depends on the route, the first person might walk straight up and whilst the second person might wonder up and down the slopes enjoying the view.

By the time they reach the top, you have no way of knowing (based just on their position now) how much work they have each done to get there, so work done is not a state function, it depends on the path the climbers take!

If we now think about the gravitational potential energy of each climber, that is simply proportional to how high the climber is on the mountain, so we can work that out when they are at the top, without knowing how they got there. So gravitational potential energy is a state function!


In chemistry the idea that enthalpy is a state function is expressed in hess's law:

'enthalpy change associated with a given reaction is independent of the route taken between reactants and products'

This means that if you can find 2 different paths between reactants and products then you know their enthalpy changes must be equal and you can use that to find previously unknown enthalpy changes. That all uses the idea of state functions