Reaction Rates & Stoichiometry
The change in the concentration of reactants or products as a function of time.
What is the reaction rate?
The exponents m and n in the rate law (Rate=k[A]m[B]n) which must be determined experimentally.
What are the reaction orders?
A substance that increases the reaction rate without itself being consumed and often provides an alternative reaction pathway with a lower total activation energy.
What is a catalyst?
When a chemical system is at equilibrium, the forward and reverse reaction rates are equal.
What is meant by the forward and reverse reaction rates are equal?
The only factor that has an effect on the magnitude of the equilibrium constant.
What is a change in temperature?
Factors affecting reaction rate, besides physical state and temperature, include the frequency and energy of collisions related to this.
What is the concentration of reactants?
The units of the rate constant depend on this characteristic of the reaction.
What is the overall order of the reaction?
A substance formed in one step of the reaction mechanism and used up in a subsequent step.
What is a reaction intermediate?
Chemical equilibrium is described as this kind of state because reactions continue to occur at equal rates, resulting in no net macroscopic change.
What is a dynamic state?
If the reaction quotient (Qc) for a reaction is 75, and the equilibrium constant (Kc) is 195, the reaction must proceed in this direction to establish equilibrium.
What is to the right (or towards the products)?
Note: Since Qc (75) is less than Kc (195), the system must increase products to reach equilibrium.
For the reaction 2NH3(g)→N2(g)+3H2(g), if the rate Δ[H2]/Δt is 0.030 mol L−1s−1, then this is the value of Δ[NH3]/Δt.
What is -0.020 mol L-1 s-1?
Note: Rate = -(1/2) * Δ[NH3]/Δt = (1/3) * Δ[H2]/Δt; Therefore: Δ[NH3]/Δt = -(2/3) * 0.030 = -0.020 mol L-1 s-1
For a first-order reaction, a plot of this quantity versus time yields a straight line.
What is ln(At) (or the natural logarithm of concentration at time t)?
The energy threshold that colliding molecules must exceed in order to react effectively.
What is the activation energy (Ea)?
A very large value for K indicates that the reaction favors these.
What are the products (or favoring the products)?
Kc and Kp will always equal one another when this is true regarding the number of moles of gas in the reaction equation.
What is when the number of moles of gaseous products equals the number of moles of gaseous reactants (Δngas=0)?
For the reaction 5Br− + BrO3− + 6H+ → 3Br2 + 3H2O, the rate expressed as Δ[Br2]/Δt is equal to this expression involving the bromate ion concentration change.
What is 3Δ[BrO3-]/Δt?
The appropriate set of units for a second-order rate constant.
What are L mol−1s−1 (or L/mol⋅s)?
The number of reactant particles involved in an elementary step.
What is molecularity?
Pure solids and liquids are excluded from the mass-action expression for Q or K in this type of equilibrium.
What is a heterogeneous equilibrium?
According to Le Châtelier’s Principle, adding an inert gas to a gas-phase system at equilibrium will have this effect on the equilibrium position, assuming the volume does not change.
What is no change (or none)?
The slope of a line tangent to the concentration versus time curve at any specific point in time.
What is the instantaneous rate?
The units for the rate constant (k) for a zero-order reaction.
What are mol L−1s−1 (or mol/L⋅s)?
In the Arrhenius equation (k=Ae−Ea/RT), the factor A is known by this name, and is the product of the collision frequency (Z) and the orientation probability factor (p).
What is the frequency factor?
If an overall reaction is the sum of two or more reactions, the overall equilibrium constant is calculated by performing this mathematical operation on the K values of the individual steps.
What is multiplication (or multiplying the K values)?
The behavior of the reaction system POCl3(g)⇌POCl(g)+Cl2(g) if POCl is added to the container.
What is the reverse reaction will proceed to establish equilibrium (or the shift is to the left)?