Orders and Rate Equations Flashcards
Reaction rate usually determines by
Concentration change with time
0 order with respect to A
Rate is unaffected by changes in A’s concentration
Rate = [A]0
Rate units
Mol dm-3 s-1
First order re: B
Rate is doubled by doubling B’s concentration
Second order re: C
Rate is quadrupled by doubling C’s concentration
Rate equation
Rate=k[A]0[B]1[C]2
k= constant of reaction
Large k vs small k
Large=fast reaction rate
Small=slow reaction rate
Graphs measure?
Half-life of a reactant
First-order concentration/time graph
Constant half-life therefore halves in equal time intervals
Even slope
Zero-order concentration/time graph
Falls at steady rate
Half-life decreases with tome
Straight negative diagonal
Second order concentration/time graph
Half life gets progressively longer, therefore increases with time
Line gets more curved
Zero order rate/concentration graph
Straight horizontal line
First order rate/concentration graph
Straight positive diagonal line
Second order rate/concentration graph
Positive sloped diagonal line
Or
Graph plotting rate/[A]2 to get straight horizontal line
Third order reaction equation
k[X(aq)]2 Y(aq)]
Rate constant equation
k= rate/[X]2[Y]
Zero order unit
Rate=k[A]0=k
Unit = mol dm-3 s-1
First order
Rate=k[A]
unit = s-1
Second order
Rate=k[A]2
Unit= dm3 mol-1 s-1
Third order
Rate=k[A]2 [B]
unit=dm6 mol-2 s-1
Rate determining step
Slowest step, main control of reaction rate
Rate equation therefore only includes reacting species of this step
Kc
Equilibrium constant
Equilibrium law
aA+bB = cC+dD
Letters are equil concentrations
Each one has its concen. raised to the power of its balancing number in the equation
Equilib concentration equaton
Products multiplied together/reactants multiplied together
Kc units
Do Kc equation but with their units instead
Kc properties
Kc=1: equil halfway between reactants and products
Kc=100: equil in favour of products
Kc=1x10-2: equil in favour of reactants
Kc is ONLY changed by altering temperature
Kc shows how far a reaction proceeds, NOT how fast
Kc temperature link
Exothermic reaction=Kc decrease with temperature increase
Endothermic reaction=Kc increase with temperature increase
I.C.E. table?
Initial/change/equilibrium
Kd, partition coefficient
Measures relative solubility of a solute between 2 solvents
Kd equation
Concentration of organic solvent/concentration in water
Non-polar organic compounds=more soluble in organic solvents than in water, therefore Kd=>1
Kp
Equil constant for gases
Kp equation steps?
1) mole fraction of A, Xa=no. of moles in A/total moles in gas mixture
2) A’s partial pressure, Pa= Xa x P (P=total pressure)
Partial pressure, p
Contribution a gas makes towards total pressure, P
Kp equilibrium constant equation
Similar to Kc, but replace concentrations with partial pressures
Kp units
Replace partial pressure value in Kp equation with the units
K
E.g 0.09=k[0.1]⁰[0.3]²
k=0.09 aka 0.11
