Equilibrium Constant: Kp | A-level Chemistry | OCR, AQA, Edexcel
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Equilibrium Constant: Kp in a
Equilibrium Constant: Kp in a Snap!
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The key points covered in this video include:
1. Partial Pressures
2. Mole Fractions
3. How do we calculate partial pressures?
4. Equilibrium constant (Kp)
5. Heterogeneous Reactions
Partial Pressures
Reaction mixtures containing gases exert a pressure on the walls of their sealed container. When we think about the pressure - the particles of gas do not interact with each other to a good level of approximation. So if we have two gases in a container the total pressure is the same as the pressures from each gas added together. We call the pressure that each type of gas would exert on its own, a partial pressure. You may see different symbols for partial pressures. We’re going to use p(A) from now on but remember you could see Pa. This same treatment extends to any number of different gases. The total pressure is the sum of the partial pressures.
Mole Fractions
So how do we quantify the amount of a reactant in a mixture? We use mole fractions - The symbol we use for a mole fraction is Xa. Mole fractions tell us the fraction of the mixture made from a particular gas, we calculate it using: Mole fraction, Xa = number of moles of substance A / total number of moles of all substances. Example: A sealed box of air contains 0.14 moles of oxygen, 0.52 moles of Nitrogen and 0.01 moles of other gases, what is the mole fraction of oxygen?
How do we Calculate Partial Pressures?
The amount of pressure a gas exerts depends on how many particles there are - more particles means more pressure. The number of moles of the gas tells us how many particles. there are: Remember there are 6.02 x 10^23 particles in a mole of substance. Because the pressure of a mixture of gases is the sum of the partial pressures and pressure is proportional to the number of particles we can write. So we can see the partial pressure is given by: p(A) = Xa x Total Pressure. Example: A sealed box of air contains 0.14 moles of oxygen, 0.52 moles of Nitrogen and 0.01 moles of the other gases, the total pressure is 140 kPa, what is the partial pressure of oxygen?
Equilibrium constant, Kp
For equilibrium reactions involving gases we can write the equilibrium expressions in terms of partial pressures rather than concentrations. This give a new type of equilibrium contants: Kp. For the general equilibrium reaction. The gas equilibrium constant is given by. Example: At equilibrium the partial pressure of dinitrogen tetroxide is 50kPa and the partial pressure of nitrogen dioxide is 68 kPa, find Kp for the reaction.
Heterogeneous Reactions
For equilibrium reactions involving more than one state, we alter the Kp expression by: Not including solids in the expression. Not including pure liquids in the expression. We only include gases if we are working out Kp.
Summary
Partial pressures are the pressure a particular species of gas would exert on its own
The sum of the partial pressures of all gases in a mixture gives the total pressure
The amount of gases in a mixture is quantified by its Mole fraction given by
Xa = number of moles of substance A / total number of moles of all substances
You can find the partial pressure of a gas in a mixture using:
p(A) = Xa x Total Pressure
We can use a new equilibrium constant for equilibriums involving gases, Kp
We don’t include solids or pure liquids in the equation for Kp
Unlock the full A-level Chemistry course at http://bit.ly/2kFPDG0 created by Barney Fidler, Chemistry expert at SnapRevise.
SnapRevise is the UK’s leading A-level and GCSE revision & exam preparation resource offering comprehensive video courses created by A* tutors. Our courses are designed around the OCR, AQA, SNAB, Edexcel B, WJEC, CIE and IAL exam boards, concisely covering all the important concepts required by each specification. In addition to all the content videos, our courses include hundreds of exam question videos, where we show you how to tackle questions and walk you through step by step how to score full marks.
Sign up today and together, let’s make A-level Chemistry a walk in the park!
The key points covered in this video include:
1. Partial Pressures
2. Mole Fractions
3. How do we calculate partial pressures?
4. Equilibrium constant (Kp)
5. Heterogeneous Reactions
Partial Pressures
Reaction mixtures containing gases exert a pressure on the walls of their sealed container. When we think about the pressure - the particles of gas do not interact with each other to a good level of approximation. So if we have two gases in a container the total pressure is the same as the pressures from each gas added together. We call the pressure that each type of gas would exert on its own, a partial pressure. You may see different symbols for partial pressures. We’re going to use p(A) from now on but remember you could see Pa. This same treatment extends to any number of different gases. The total pressure is the sum of the partial pressures.
Mole Fractions
So how do we quantify the amount of a reactant in a mixture? We use mole fractions - The symbol we use for a mole fraction is Xa. Mole fractions tell us the fraction of the mixture made from a particular gas, we calculate it using: Mole fraction, Xa = number of moles of substance A / total number of moles of all substances. Example: A sealed box of air contains 0.14 moles of oxygen, 0.52 moles of Nitrogen and 0.01 moles of other gases, what is the mole fraction of oxygen?
How do we Calculate Partial Pressures?
The amount of pressure a gas exerts depends on how many particles there are - more particles means more pressure. The number of moles of the gas tells us how many particles. there are: Remember there are 6.02 x 10^23 particles in a mole of substance. Because the pressure of a mixture of gases is the sum of the partial pressures and pressure is proportional to the number of particles we can write. So we can see the partial pressure is given by: p(A) = Xa x Total Pressure. Example: A sealed box of air contains 0.14 moles of oxygen, 0.52 moles of Nitrogen and 0.01 moles of the other gases, the total pressure is 140 kPa, what is the partial pressure of oxygen?
Equilibrium constant, Kp
For equilibrium reactions involving gases we can write the equilibrium expressions in terms of partial pressures rather than concentrations. This give a new type of equilibrium contants: Kp. For the general equilibrium reaction. The gas equilibrium constant is given by. Example: At equilibrium the partial pressure of dinitrogen tetroxide is 50kPa and the partial pressure of nitrogen dioxide is 68 kPa, find Kp for the reaction.
Heterogeneous Reactions
For equilibrium reactions involving more than one state, we alter the Kp expression by: Not including solids in the expression. Not including pure liquids in the expression. We only include gases if we are working out Kp.
Summary
Partial pressures are the pressure a particular species of gas would exert on its own
The sum of the partial pressures of all gases in a mixture gives the total pressure
The amount of gases in a mixture is quantified by its Mole fraction given by
Xa = number of moles of substance A / total number of moles of all substances
You can find the partial pressure of a gas in a mixture using:
p(A) = Xa x Total Pressure
We can use a new equilibrium constant for equilibriums involving gases, Kp
We don’t include solids or pure liquids in the equation for Kp
5 سال پیش
در تاریخ 1398/06/20 منتشر شده
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