The vapor pressure of water at 25 °C is 0.0313 atm. Cal- culate the values of Kp and Kc at 25 °C for the equilibrium H2O1l2 ∆ H2O1g2.

Video transcript

Hello. In this problem, we are told that 63.5°C, Ethanol has a vapor pressure of .5-6 atmospheres. We are asked to determine the equilibrium constant in terms of pressure and concentration for the equilibrium between Ethanol as a liquid and ethanol as a gas. Let's begin by writing the equilibrium constant in terms of pressure. So it will be equal to the pressure of our products, which would be that's an all in the gas phase. And we do not include pure liquids. So we eliminate then the ethanol as a liquid from our equilibrium cost and expression this then, as we're told in the crime statement, the vapor pressure of ethanol is 0.5 to six atmospheres. Now let's find the equilibrium costs in terms of concentration it will be equal to the concentration then of ethanol. In the gas phase. We can relate the equilibrium constant in terms of concentration to that in terms of pressure. By making use of the ideal gas equation. So if we get moles volume to one side, it equals pressure over the gas constant times temperature. So on the left hand side this is concentration and so our K. C. Value then will be equal to K. P. Over R. T. Keep in mind or recall the general formula that relates R. K. P to R K. C. The equilibrium cost in terms of pressure is equal to that in terms of concentration, times gas costs at times temperature to the delta N. Where delta N. Is equal to the moles of gaseous products minus moles of gaseous reactant, Which in our case is equal to 1 0, so it's equal to one. So we come up with the same relationship that our equilibrium constant in terms of concentration is equal to that in terms of pressure, divided by the gas constant, divided by temperature. So our equilibrium costs are in terms of concentration then is equal 0.5-6 atmospheres, Divided by the gas constant 0.08206 leaders atmospheres per Kelvin Mole And our temperature in Kelvin is 336.5. So including units does help us to make sure that we have the correct units of pressure and temperature, but the units will not cancel to anything meaningful recall that our equilibrium constant does not have any units. So our equilibrium constant in terms of concentration works out to 0.0190. So our equilibrium constant in terms of concentration can be found by relating it to the equilibrium constant in terms of pressure And our equilibrium constant in terms of pressure was found to be 0.5 - six atmospheres. Thanks for watching. Hope this helped