Reaction Rates and Equilibria Flashcards
3 conditions required for a reaction to occur
- collision
- orientation: reactants must align properly to break and form bonds
- energy: the collision must provide the energy of activation
rate of the reaction equation
rate of reaction = change in concentration of reactant or product/ time
factors that affect the rate of reaction
- change in temperature
- change in reaction conc
- adding a catalyst
what happens to the rate of reaction when increasing the temperature
there is an increase in the KE of the reactant molecules, which makes them move faster, makes them collide more often, and makes them collide with more energy
what happens to the rate of reaction when increasing the reactant concentration
when there are more reacting molecules, more collisions that form products can occur and the reaction goes faster
what happens to the rate of reaction when you add a catalyst?
speeds up the rate of the reaction of both the forward and reverse reactions by the same amountsk by providing an alternative pathway that has a lower activation energy. As a result, more collisions provide sufficient energy for reactants to form product
activation energy
the minimum amount of energy required to break the bonds between atoms of the reactants
what happens to k as you decrease activation energy?
the smaller the Ea the larger the k
molecularity
the number of molecules that must collide to generate product
half-life in a chemical reaction
the time required to halve the reactant concentration
the half-life for a first-order reaction
t1/2 = ln2/k
the half-life for a second-order reaction
t1/2 = 1/k[A]0
dynamic equilibria
the reaction keeps happening both forward and reverse at the same rate
equilibrium conditions
- The rate of forward reaction is equal to the rate of the reverse reaction
- the forward and reverse reactions continue at the same rate
describe the properties of an equilibrium constant for a reversible chemical reaction
- it is a fixed value at a specific temperature
- the value that the system will evolve to reach an equilibrium
what is activity
the effective molar conc of a species in the solution
Kc
the numerical value obtained by substituting experimentally measured molar concentrations at equilibrium into the expression
large Kc
large amounts of products produced from the forward reaction
small Kc
low concentration of products and high concentration of reactants
reaction quotient Q
uses non-equilibrium concentrations
Q< Kc
more products will be synthesized
Q> Kc
the reaction proceeds to the left
le chatelier’s principle
when a stress is placed on a reaction at equilibrium the system responds by changing the rate of the forward or reverse reaction in the direction that relieves that stress
k -1
the kinetic rate of the reverse reaction
what is the relationship between the 2 rate constants of the forward and the reverse reaction?
k1/k-1 = Kc
the rate is numerically identical to the equilibrium constant
what is Ea (forward) - Ea (reverse) equal to
E (forward) - E (reverse)
what state do catalysts decrease?
the transition state
what does oxygen transport involve
an equilibrium between hemoglobin Hb, oxygen, and oxyhemoglobin HbO2
Chatelier’s principle of oxygen in water
oxygen is poorly soluble in water and so the equilibrium is in favour of the formatio of oxygen gas and not aqueous oxygen: the equilibrium shifts to the left
O2 + H2O (equilibrium sign) O2
how can we perturb the equilibrium of oxygen in water
by addition of hemoglobin which gives rise to oxyhemoglobin: the concentration of oxygen that is free decreases because it is bound to haemoglobin
what happens when there is a high pressure of oxygen in the alveoli
the reaction shifts in the direction of oxyhemoglobin
what happens when there is a low pressure of oxygen in the tissues
the equilibrium shifts to release oxygen from HbO2
what happens at normal Patm
oxygen diffuses into the blood because the partial pressure of oxygen in the alveoli is higher than in the blood.
what happens at a decrease in Patm
results in a lower pressure of oxygen which means less oxygen is available for the blood and body tissues
the equilibrium constant for hemoglobin
Keq = [HbO2]/[Hb]p^4 O2
oxygen gas binds with a 1: 4 stoichiometry (1Hb: 4O2)
what happens at an altitude of 18,000ft
a person will obtain 29% less oxygen and may result in hypoxia
hypoxia
respiratory rate, headache, fatigue
what happens when there is a general decrease of oxygen in the air
the equilibrium will shift in the direction of the reactants thus depleting the conc of HbO2
thermodynamics
measure of energies
state variables
define the conditions of a reaction in regard with pressure, volume, temperature and chemical composition
system
the reaction mixture we have: where the reaction takes place
1st law of thermodynamics
the change of the internal energy of a closed system equals to the heat supplies to the system minus the work done by the system
internal energy U
a state function that represents all the internal energy present in our reactants, products and molecules
variation of internal energy of a state
ΔU = q + w
q= heat released/supplied by the system
w= work done on/by the system
how can work be manifested in chemistry
by observing a change in volume
w = -pe ΔV
pe = external pressure
what is the variation of enthalpy at a constant pressure equal to?
the heat exchange
ΔH = q
enthalpy
comes from the combination of internal energy, pressure and volume and its variation is equal to heat.it is a state function and an extensive property
extensive property
it depends on the state and size of the system
what does the variation of enthalpy represent
the heat released or absorbed during a chemical reaction
units of enthalpy
kJ/mol
what does ΔHo mean
it is measured at the standard state (1atm, 298.15 K, and the solutions 1M)
second law of thermodynamics
spontaneous processes are characterized by an increase in the disorder of the universe (entropy)
what happens to the variation of entropy in spontaneous processes
the variation of entropy is equal or greater than the ratio between the heat exchange and teh temperature
ΔS > q/t
when is a reaction spontaneous
ΔH - TΔS < 0
free energy
state function introduced by gibbs and it refers to the energy exchanged throughout a chemical reaction
equation for gibbs free energy
ΔG = ΔH - TΔS
ΔG < 0
exergonic and it occurs spontaneously
ΔG > 0
endergonic and it requires an external input of energy to occur
variation in the free energy in a chemical reaction
ΔG = ΔGo + RTlnQ
free energy variation knowing the equilibrium constant
ΔGo = -RTlnK
equilibrium constant is temperature-dependent
lnk = -ΔH/R (1/T) + ΔS/R
what needs to be overcome to reach the products
the transition state
