Kinetics and equilibrium in chemical reactions Flashcards
How is the overall rate of a chemical reaction obtained?
Dividing the rate of formation or disappearance of a given product or reactant (respectively) by the corresponding stoichiometric coefficient
What is an elementary process?
An individual reaction in a detailed mechanism (from an overall reaction). Any reaction proceeds through some mechanism which is generally impossible to predict from its chemical equation. Each step proceeds at its own rate. The rate of the overall reaction is naturally limited by the slowest step (rate-determining step)
In an elementary process, the orders with respect to the reactants, are equal to the corresponding stoichiometric coefficients.
True or false? The overall reaction rate law is equal to the rate law of the rate determining step
true
What is the activation energy of a chemical reaction?
The energy it takes to get the reaction started.
If the collision energy of two molecules is not sufficient (ie. does not meed the EA), a reaction will not happen.
What is the species formed during an efficient collision, before the reactants transform into the final product(s) is called what?
The activation complex or the transition state
What is a thermodynamically controlled reaction? Kinetically controlled reaction?
Thermodynamically controlled: If the reactants exclusively perform the reaction that forms the most thermodynamically stable product (eg. lowest Gibb’s free energy)
Kinetically controlled: If the reactants exclusively perform the reaction that forms the product that is produced more quickly.
Give the formula for the rate of an enzyme catalysed reaction and explain it.
rate = k[ES]
The enzyme/substrate concentrations determine the rate of the reaction (rather than the rate limiting step within the reaction), because of enzyme saturation kinetics.
True or false? Catalysts speed up the rate of reaction without affecting Keq
true
What does Le Chatelier’s principle state about pressure and gases?
That whenever a perturbation is applied to a system at equilibrium, the system evolves in such a way as to compensate for the applied perturbation.
An increase in total pressure (decrease in volume) favours the direction which decreases the total number of compressible (ie gases) moles (eg. from the left hand side where there are 4 moles to the right hands side where there are 2 moles)
It can also be said that when there are different forms of a substance, an increase in total pressure (decrease in volume) favours the form with the greatest density, and a decrease in total pressure (increase in volume) favours the form with the lowest density.
How does change in temperature effect equilibrium, according to Le Chatelier’s principle?
If the temperature of a reaction mixture at equilibrium is increased, the equilibrium evolves in the direction of the endothermic reaction.
How is change in standard Gibb’s free energy calculated with the equilibrium constant (Keq)?
ΔG° = -RT(LnKeq)
How does the solubility of Pb(OH)2 in water differ for a solution at pH of 7 and pH 9?
Pb(OH)2 ⇋ Pb+2 + 2OH-
At pH 9, the concentration of OH- ions from water is higher than at pH 7. Thus, according to Le Chatelier’s principle, the additional common ion (OH-) will push the equilibrium to the left and less Pb(OH)2 will dissolve (Ie. solubulity decreases)
Cations can be added to solutions to precipitate anions out (and vice versa). Anions will be sequentially precipitated out of solution depending on ___?
Anions will be ionically bonded to the cation and precipitate out first if they form the LEAST soluble product.
For example, a solution that contains PbSO4, PbCO3 and PbI2 can be treated with extra Pb+2. Because PbCO3 is least soluble, it will precipitate out first, then PbI2 and then PbSO4. The solubilities of these compounds are normally revealed somehow in the passage.
In the second step of preparing H2SO4 from elemental sulfur (the catalytic oxidation of SO2), which strategy is most likely to increase the yield of SO3 formed?
- Reducing the reaction temp
- Reducing reaction pressure
- Removing SO3 from reaction mixture
- Removing O2 form reaction mixture
- Removing SO3 from the reaction mixture
According to Le Chatelier’s principle, any action that causes the reaction to shift towards the right will cause O2 and SO2 to react and increase the yield of SO3. Of the four possible actions, the removal of SO3 as it forms will shift the reaction towards to the right and is the most likely action to increase the yield of SO3.
How is the rate constant, k, effected by activation energy?
Greater activation energy (required) would decrease k, since fewer molecules would have the necessary kinetic energy to proceed with the reaction.
