[CHM] partial pressure

Discussion in 'DAT Discussions' started by ippie, Jun 4, 2008.

1. ippie ippie

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#1. "the partial pressure of one gas in a mixture is independent of the other in the mixture."
Is this statement true or false?
I think it's false.
The partial pressure of one gas is the product of total pressure and mole fraction of that gas.
Mole fraction is dependent of the proportion of one gas and the other gas.
Therefore, the statement given is false. right?
BUT THE ANSWER IS TRUE. WHY?

#2. catalysts have which of the following effect on chemical reactions?
a. increase the rate at which product is formed.
b. lower the energy of formation of the products.
==> of course, a is right, but why not b? the energy mentioned in B is activation energy or enthalpy? If it is activation energy, then B can also be the answer, but if it is enthalpy, B cannot be the answer. how can we tell??

#1
Last edited: Jun 4, 2008

3. zriceman Member

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#2 b, i think Energy of Formation is Change in H with f as the subscript. So it is a value of enthapy, which would make B not the correct answer.

This is what i think at least. Any one else?

4. nt4reall New Member

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Pa= Xa x Pt *
Xa = na/ nt
Therefore Pa= (na/nt)Pt
nt is total moles of all different gas
nt= na + nb + nc + nd +...
the more gases (a, b, c , d, e...)in the solution , the more nt , and the less mole fraction of Xa ( a constant) , the less Pa (*)
the less gases in the solution , less nt , and Xa increases , therefore Pa increases.
That means "the partial pressure of one gas in a mixture is dependent of the other in the mixture."
Because the first statement said independent , therefore this statement is wrong.
"The partial pressure of one gas is the product of total pressure and mole fraction of that gas." True

5. Optimism Smiles DAT drains my ATP

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#1. If the two gases are not interacting CHEMICALLY, they will act independently of the other.

6. drgreen

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#1, A gasses partial pressure is the pressure which the gas would have if it alone occupied the volume. My guess is since we are used to obtaining the partial pressure from a question involving total pressure and a molar fraction, we are not used to thinking in terms of what partial pressure is exactly.

7. Sea of ASH

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#1 is definately false
#2 a cataylst does not lower the engery of product formation. it lowers the activation energy as you said but what is the activation energy? its the energy required to form the transition state intermediate, not product!!!

8. smile101

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The Wiki def of partial pressure is: In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume.

I would think if the mole fraction of a gas would increase, the total pressure would increase too and therefore the overall partial pressure exerted by one gas would still be the same.
I always understood the partial pressure of one gas to be independent of others in the mixture.

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