Equilibrium 2 Flashcards
For equations involving pressure, equilibrium constant can be expressed in terms of what as well as concentration?
Pressure
What is partial pressure?
The pressure a gas in a mixture would exert if it alone occupied the volume of the mixture
How can the partial pressure of a gas be calculated?
p(x) =( n(x) / n(total)) x Ptotal
What is the only variable that can affect the value of an equilibrium constant?
Temperature
Why does changing concentration of a reactant or product not have an effect on the equilibrium constant?
Changing the concentration of one or more reactants or products means that the reaction would no longer be in an equilibrium state, so no equilibrium means there would be no equilibrium constant
What is dynamic equilibrium?
When the forward and backwards reactions are happening at the same rate, so the concentrations of reactants and products stays constant
How are moles at equilibrium calculated?
Reactants: initial moles - moles reacted
Products: initial moles + moles formed
How can total pressure be calculated from partial pressures?
Adding all partial pressures together
How is mole fraction calculated?
number of moles of a gas / total number of moles of all gases
What value of Kc indicates that the reaction does not go?
Kc < 10^-10
What value of Kc indicates that the reactants predominate at equilibrium?
Kc ≈ 0.1
What value of Kc indicates an equal amount of products and reactants?
Kc ≈ 1
What value of Kc indicates that products predominate at equilibrium?
Kc ≈ 10
What value of Kc indicates that reaction goes to completion?
Kc > 10^10
What is the effect of changing pressure on Kp?
Kp stays constant, but position of equilibrium will alter to maintain the value
Why does a catalyst have no effect on Kp or Kc?
It speeds up the rates of the forward and reverse reactions by the same amount
Why are industrial processes not in equilibrium?
Products are removed as they are formed to improve conversion of reactants, so they are not closed systems
How does simple paper chromatography separate mixtures?
The solvent moves up the paper by capillary action, and substances with greater affinity for the mobile phase (the solvent) move further up the paper than substances with greater affinity for the stationary phase.
Substances are in equilibrium between the mobile phase and the stationary phase, and how close the equilibrium is to the stationary or mobile phase determines how fast they move
How is an Rf value calculated?
Dividing the distance travelled by each separate substance by the distance travelled by the solvent in that experiment
Why are Rf values useful?
They can compare the results of different chromatograms
What can gas chromatography be used to separate?
Mixtures of volatile liquids - the most volatile component is the first peak in the graph
What is retention time?
The time taken for a particular compound to
travel from the injection of the sample to where
it leaves the column to go to the detector
What is the mobile phase of gas chromatography?
Usually inert Helium gas - the gas that carries the components
What is the stationary phase of gas chromatography?
The solid inside the column, which is often things like silica, but changes
What affects retention time in gas chromatography?
How much the components interact with the mobile phase - less interaction = faster chromatography
Why is the column in gas chromatography a spiral?
It saves space
What is the mobile phase of high performance liquid chromatography?
The liquid - forced through by high pressure pumps
What is the stationary phase of high performance liquid chromatography?
The solid, often things like silica, and but it is often modified to change the polarity
What can a combination of gas chromatography and mass spectrometry be used for?
To identify substances precisely - for example, can be used in drugs testing
