17. Equilibrium HL

Describe the equilibrium established between a liquid and its own vapor and how it is affected by temperature changes?

A liquid in an enclosed chamber will form equilibrium with its own vapor

Fast moving particles in the liquid will escape from the liquid and become part of the vapor

Slow moving particles in the vapor will re-join the liquid.

As temperature increases, vapor pressure increases

Sketch graphs showing the relationship between vapor pressure and temperature and explain them in terms of the kinetic theory AND State and explain the relationship between enthalpy of vaporization, boiling point, and IMF’s

Vapor pressure increases with temperature because the average amount of energy in each particle is higher, so more escape the liquid and enter the vapor state

Enthalpy of vaporization- the amount of energy needed to change 1 mol of liquid à gas at standard temp + pressure

When enthalpy of vaporization is high, the vapor pressure is low

            This is because there are strong intermolecular forces (as more energy is needed to break those bonds and vaporize the substance). This means that boiling points are high, so fewer particles will enter the vapor state

When enthalpy of vaporization is low, the vapor pressure is high

            This is because there are weak intermolecular forces (as less energy is needed to break those bonds and vaporize the substance). This means that boiling points are low, and more particles will enter the vapor state

Solve homogenous equilibrium problems using the expression for K_c

EXAMPLE!!!

A mixture of nitrogen monoxide and oxygen forms an equilibrium with the product, nitrogen dioxide. If there are 0.03 moldm^-3 NO, 0.04 moldm^-3 O₂, and 0.02 moldm^-3 of NO₂, what is the value of K_c

First, find the equation

2NO + O₂ à 2NO₂

Then, write the expression for eq

K_c =    [NO₂]²    _.

       [NO]²[O₂]

Next, substitute the concentrations and calculate

K_c =    [0.02]²    _{. =} 0.0017777… = 1.78 x 10^-3

       [0.03]²[0.04]

Finally, find the units by finding the overall order. Because this is 2^nd order divided by 3^rd, it becomes this non existent -1^st order. We can determine the units by bringing back our old chart from kinetics…

Zero	mol1 dm-3
First	mol0 dm0
Second	mol-1 dm3
Third	mol-2 dm6

And going backwards to find that it would be in mol²dm^-6

NOTE: That unlike the units from Kinetics, there is no sec^-1 factor. This is because equilibrium does not take time into account. DO NOT MENTION TIME WHEN TALKING ABOUT EQUILIBRIUM