* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download printable version
Pseudo Jahn–Teller effect wikipedia , lookup
Electrochemistry wikipedia , lookup
Asymmetric induction wikipedia , lookup
Supramolecular catalysis wikipedia , lookup
Multi-state modeling of biomolecules wikipedia , lookup
Colloidal crystal wikipedia , lookup
Acid dissociation constant wikipedia , lookup
Nucleophilic acyl substitution wikipedia , lookup
Photoredox catalysis wikipedia , lookup
Hydrogen-bond catalysis wikipedia , lookup
Process chemistry wikipedia , lookup
Thermomechanical analysis wikipedia , lookup
Marcus theory wikipedia , lookup
Physical organic chemistry wikipedia , lookup
Ring-closing metathesis wikipedia , lookup
Photosynthetic reaction centre wikipedia , lookup
Ultraviolet–visible spectroscopy wikipedia , lookup
Vapor–liquid equilibrium wikipedia , lookup
Thermodynamics wikipedia , lookup
Strychnine total synthesis wikipedia , lookup
Stability constants of complexes wikipedia , lookup
George S. Hammond wikipedia , lookup
Lewis acid catalysis wikipedia , lookup
Chemical reaction wikipedia , lookup
Thermodynamic equilibrium wikipedia , lookup
Bioorthogonal chemistry wikipedia , lookup
Click chemistry wikipedia , lookup
Rate equation wikipedia , lookup
Chemical thermodynamics wikipedia , lookup
Stoichiometry wikipedia , lookup
Transition state theory wikipedia , lookup
1/14/2014 CHEMICAL EQUILIBRIUM Unit #11 Chapter 13 Equilibrium • Equilibrium occurs when the rate of the forward reaction is equal to the rate of the reverse reaction • Equilibrium is a dynamic state, this means that even though it seems that the reaction has stopped, in fact the products are still being made and used up-but at the same speed (rate). • Equilibrium is symbolized by the use of a double arrow ( ) or an equals sign (=) Equilibrium, continued • At the point when equilibrium occurs in a chemical reaction, some reactants has been converted to products. • The amounts depend on the reaction and are most often described in Molarity (mol/L) • Because of this use of measurement; solids, liquids and water are not considered in calculations. • Solids and liquids are pure and have no concentration and of course water is a liquid. • Each reaction has its own set of conditions that must be met and it is the same for the reaction (always) based on temperature. 1 1/14/2014 How Equilibrium is Measured • Each reaction that is reversible and therefore, can reach equilibrium, is assigned a constant, Kc. • Kc = equilibrium constant has no units and tells the ratio of concentrations (in M) at equilibrium. That is what the “c” stands for. • Sometimes, just “K” is used and this is the same as Kc or Keq which also is molarity dependent. Equilibrium is not for everyone! • Some reactions go to completion and are not reversible. • These reactions show only a forward arrow. • Equilibrium (reversible) reactions must happen in a closed container. • All gases are considered because their concentration changes by the size of the container. How is Kc Calculated • When equilibrium occurs, the concentration of the products and reactants are used to determine the equilibrium constant (Kc). • Let’s look at a reaction at equilibrium … H2(g) + I2(g) 2 HI(g) The equilibrium expression is … Kc= [HI]2 [H2][I2] it is measured in the concentrations of the products (raised to the coefficient power) divided by the concentration of the reactants (raised to the coefficient power) – excluding liquids and solids 2 1/14/2014 What are the equilibrium expressions for these reactions? 1. AgCl(s) Ag+(aq) + Cl-(aq) answer = Kc = [Ag+][Cl-] 2. 2 NH3(g) N2(g) + 3 H2(g) answer Kc = [N2][H2]3 [NH3]2 3. Pb(l) + H2O(g) PbO(s) + H2 (g) Kc = [H2] [H2O] In this case since water is a gas it is included! Kc, Kp and Q • Kc = equilibrium constant using concentrations • Kp = equilibrium constant using partial pressures and is related to Kc but not always equal to Kc • Kp is always calculated using Atmospheres (atm) • Q = the ratio of products and reactants using the same formula as Kc but means that the reaction is not necessarily at equilibrium. (Instantaneous) • If Q<Kc the reaction still needs to proceed forward to achieve equilibrium and if Q> Kc then the reaction must go in reverse to achieve equilibrium if Q=Kc the reaction is at equilibrium Calculating Kc What is the equilibrium constant for this reaction at 250 oC? 2 HI(g) H2(g) + I2(g) [HI] = 1.5 x 10-2 M and [H2] = [I2]= 3.4 x 10-3 M Answer Kc = [H2][I2] = (3.4 x 10-3 M)2 = 0.051 [HI]2 (1.5 x 10-2 M)2 3 1/14/2014 Calculating Kp • Kp is calculated the same way if all your data is given in partial pressures at 25 o C. • For example: What is the Kp for the reaction of N2(g) + 3 H2(g) 2 NH3(g) at equilibrium the partial pressures are as follows; pN2 = .0223 atm, pH2 =.0669 atm and pNH3 = 1.97 atm. • Answer • Kp = (pNH3)2 = (1.97 atm)2 = 5.81 x 105 (pN2)(pH2)3 (.0223)(.0669)3 Calculating Kp, continued • If you are trying to determine the relationship between Kc and Kp you must use a factor called ∆n. • ∆n = total moles of gaseous products – total moles of gaseous reactants • Kp = Kc(RT) ∆n • Kc = 3.48 x 108 Comparing Q and K 3 H2(g) + N2(g) = 2 NH3(g) Kc= 5.9 At a certain time the following data was gathered…[H2] = 1.19 M, [N2] = .0515 M and [NH3] = 2.27 M… Is the reaction at equilibrium? If not which direction must the reaction shift to get to equilibrium? ANSWER: Q = 59 so it is NOT at equilibrium Reaction needs to shift reverse or 4