GenChem5 (Kinetics and Equilibrium) Flashcards
A molecule in a mechanism that does not appear in the overall reaction because it is neither a reactant nor a product
intermediate
The slowest step in a reaction is called the _____
rate determining step
what are two definitions of the rate of a reaction?
decrease in reactants/time
increase in products/time
In the reaction 2A + B —> C, relate all of the rates for each molecule
(-1/2)Δ[A]/Δt= -Δ[B]/Δt = Δ[C]/Δt
A reaction that has a constant rate and is therefore independent of reactants’ concentrations is what type of reaction?
Zero-order reaction
A reaction that has a rate that is proportional to one reactant is a
First order reaction
Decay is what order of reaction?
What is the equation for radioactive decay?
First order
A=(Ao)e^-kt
What is the equation for the half life of a reaction?
t(1/2) = ln(2)/k = 0.693/k
A reaction that has a fractional order is called a
mixed order reaction
A reaction with a rate proportional to the product of the concentration of two reactants or the square of the concentration of a single reactant is a
What are the units of second order rate constants
Second order reaction
M^-1)/(s^-1
A reaction with an order greater than 2 is called a
higher order reaction
Theory stating that the rate of a reaction is proportional to the number of collisions per second between the reacting molecules
Collision theory of chemical kinetics
The minimum energy of collision necessary for a reaction to take place is called the
Activation energy, Ea, or energy barrier
What is the rate in terms of number of collisions?
rate=fZ
Z= number of collisions, f= fraction of effective collisions
A collision where molecules collide with the correct orientation and sufficient force to break the existing bonds and form new ones.
Effective Collision
Occurs after a collision with sufficient energy, a state in which the old bonds are weakened and the new bonds begin to form
Transition state
What is the other term for the transition state, which have an extremely short, finite lifetime?
Does it have a greater or lesser energy than the reactants/products?
Activated complex
It has a greater energy
A negative enthalpy (ΔH) indicates what type of reaction?
A positive ΔH indicates what type of reaction?
Exothermic
Endothermic
Where does the activated complex exist on a potential energy diagram?
At the top.
What is the difference between the potential energy of the products and reactants?
ΔH, enthalpy change
How does greater concentration of reactants affect the reaction rate?
Increases the rate
How does higher temperature affect reaction rate?
Increases the rate (higher avg KE, more molecules with Ea)
Can the medium effect the rate of the reaction?
Yes.
Substances that increase the reaction rate without themselves being consumed
Catalysts
How do catalysts affect the activation energy?
Catalysts lower the activation energy
What is the equilibrium constant, Kc, for the following one step reaction:
2A=B+C
Kc=([B][C])/[A]^2
If a reaction quotient, Q, is constant, what can be said about the reaction
It is in equilibrium, and Qc = Kc
Do pure solids and liquids appear in the equilibrium constant?
No.
Does Keq remain constant at different temperatures?
No.
If Keq is much larger than 1, are there more reactants or products?
Products
If less than one, more reactants
If Keq is close to one, what can be said about products and reactants?
They are equal and approximately in equilibrium
Does changing the pressure affect the volume of all substances?
No, mainly gases because they are highly compressible
How are pressure and volume related?
Inversely
In the following system:
A–>B + heat
What would happen if it were placed in an ice bath?
What about if it were placed in boiling water?
The temperature would decrease and equilibrium would shift to the right
Equilibrium would shift to the left
What is the only thing that can alter the equilibrium constant of a reaction?
Temperature. Not concentration, pressure, volume, etc.
