[Aetos]

The free energy change for the addition of water to fumarate to produce malate (part of the TCA cycle,.i.e metabolic breakdown pathway to produce energy from glucose) is -3.7 kJ mol-1.  What is the equilibrium constant for this reaction at 37oC?  What can you conclude from the value?

C4H2O42-   +    H2O C4H4O52-  ---->  C4H4O5 -2
   fumarate        water        <----          malate



I have read and read and read all day since I got up, and nothing is sinking in. I just dont understand anything to do with this topic. All I ask is for you to help me understand by dumbing it down for me.

[UG]

You need to use the formula  ΔG = -RT ln K.
You are given ΔG and temperature and R is just a constant so you can work out K (the equilibrium constant). Now the value of K will be very large and positive so this means the reaction is very product favoured, ie, lots of malate will be formed in the reaction.

[Aetos]

i dont understand. What is the ΔG value?

is it -3.7 kJ mol-1?

Im guessing the T value is  37*C  converted into Kelvin


but what is the R value? or is that the value I have to work out by rearranging the equation

so it would be  R=-ΔG/T
                         -3.7 /310= -0.0119354839

The answer isnt large or positive.

So how do I work out K (the equilibrium constant) if it's not in the equation?

And what do you mean by R is just a constant? what is the value for R?

[poca]

R is a constant means it is defined as a number, look in  your book or google for R.

Also K is in the equation reread what UG posted

ΔG = -RT ln K

[Aetos]

I dont have a book :/ and google gives different values for R

And If I understood what UG posted then I wouldnt be questioning what he said.


i dont know what

delta G equals minus R constant multiplied by temperature in equilibrium constant means(ΔG = -RT ln K)

This is my first time studying this topic so please dumb it down for me. even giving an example question with the answers would help.

[Borek]

I dont have a book :/ and google gives different values for R

Value of R depends on the units - just like distance changes when expressed in meter or feet.

http://en.wikipedia.org/wiki/Ideal_gas_constant

[Aetos]

oh i see

and now i also see where K comes in i didnt realise 'ln' was natural log I though it said 'in' >.<


now i need help rearranging this equation to get K :/

[Dan]

now i need help rearranging this equation to get K :/

I showed you that rearrangement in the 6th post in this thread:

http://www.chemicalforums.com/index.php?topic=52128.0

[Aetos]

oh oh! i see! so they are both worked out the same way! thank you!!!!!!!

[Aetos]

just checking if this is right

K = e -(  G/RT)

e- = e^ or e to the power (e is on the calculator)

convert -3.7 kJ mol-1 to J mol-1 = -3.7 x 1000= -3700

R constant is 8.314 JK-1mol-1

convert 37*C to kelvin= 310

then subsitute values into equation

K= e to the power -(-3700/(8.314x310))

K = e to the power –(-1.436)

K= e ^(1.436)

K= 4.20

[UG]

Looks good 
So much for K being a large number my mistake!

[Dan]

I agree with K = 4.20, nicely done.

So what can you conclude from that value?

Hint: What is the definition of K?

[Aetos]

@ UG - its all good =]


@ Dan- hmmm K is the equilibrium constant but im not sure what i conclude from that value. perhaps that the reaction is reversable? not sure >.<

[Dan]

hmmm K is the equilibrium constant but im not sure what i conclude from that value. perhaps that the reaction is reversable?

Yes, but what is an equilibrium constant? What is it a measure of?

The fact that the equilibrium constant is not extremely large or extremely small does indicate the reaction is readily reversible. You could comment on the ratio of malate and fumarate at equilibrium to extend your answer.