8.1 reaction rate
TRANSCRIPT
REACTION KINETICS8.1 REACTION RATE
LEARNING OUTCOMES:
• Define reaction rate
• Explain the graph of concentration against
time in relation to reaction rate
• Write differential rate equation
• Determine the reaction rate based on a
differential equation
What does rate of reaction mean?The speed of different chemical reactions . Some reactions
are very fast and others are very slow.
What is the rate of these reactions?
The speed of a reaction is called the rate of the reaction.
rusting baking explosion
slow fast very fast
rate = -D[A]
Dt
rate = + D[B]
Dt
A B
? ?
?
?
Reaction rate is speed of chemical reaction which is the change in the concentration of a reactant or a product with time.
What is the unit for reaction rate?kg
molal
mol L-1
s-1
dm-3
oC
mol L-1s-1
nm Ms-1
Newton
molmeter
mol dm-3 s-1 Kelvin kJ mol-1 gram
mol L-1min-1
a A + b B ® c C + d Drate = -1 d[A] = -1 d[B] = +1 d[C] = +1 d[D]
a dt b dt c dt d dt
Differential rate equation / Rate expressions
O3(g) + NO(g) ® NO2(g) + O2(g)
dt
]Od[+ =
dt]NOd[
+ = dt
d[NO]- =
dtOd
- = rate 223
Differential Rate Equation Example1:
2 NOCl (g) 2 NO + Cl2 (g)
dt
d[Cl+ =
dt
d[NO] =
dt
NOCld- = rate
]
2
1
2
1 2
2 moles of NOCl disappear for every 1 mole Cl2 formed.
Differential Rate Equation Example2:
Rate of disappearance of NOCl is twice as fast as the rate of formation of Cl2
Differential Rate Equation Question 1:
Write the differential rate equation for the following reactions:(a) I-(aq) + OCl-(aq) Cl-(aq) + OI-(aq)
(b) 3O2(g) 2O3(g)
(c) 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)
Differential Rate Equation Challenging Question 1:
(a) N2O5(g) 2NO2(g) + ½ O2(g)
(b) 2H2O2(aq) 2H2O(l) + O2(g)
Write the rate expression for the following reaction:
(c) 4NH3 (g) + 5O2 (g) 4NO (g) + 6H2O (l)
Write the differential rate equation in the term of changes in pressure with time
(d) 2NOBr (g) 2NO (g) + Br2 (g)
Differential Rate Equation Example 3:
C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(g)If the ethane, C2H6 is burning at the rate of 0.20 mol dm-3s-1. Calculate the rate offormation of CO2
STEP 1: Write the differential rate equation for the substances that related to the question
STEP 2: Substitute the given information into the differential equation
?
dt
COd
dt
HCd ][
4
1][ 262
)20.0(4][ 132 smoldm
dt
COd
13280.0
][ smoldmdt
COd
Rate of formation of
CO2 is 0.80 moldm-
3s-1
C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(g)If the ethane, C2H6 is burning at the rate of 0.20 mol dm-3s-1. Calculate the rate offormation of CO2
Student common mistakes:
dt
COd
dt
HCd ][
4
1][ 262
dt
HCd
dt
COd ][][
4
1 62 2
dt
HCd
dt
COd ][4
][ 62 2
)20.0(4][ 132 smoldm
dt
COd
13280.0
][ smoldmdt
COd
Differential Rate Equation Example 4:
C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(g)If the ethane, C2H6 is burning at the rate of 0.20 mol dm-3s-1. Calculate the rate ofdisappearance of O2
STEP 1: Write the differential rate equation for the substances that related to the question
STEP 2: Substitute the given information into the differential equation
?
dt
Od
dt
HCd ][
7
1][ 262
)20.0(7][ 132 smoldm
dt
Od
13240.1
][ smoldmdt
Od
Rate of disappearance
of O2 is 1.40 moldm-3s-1
C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(g)If the ethane, C2H6 is burning at the rate of 0.20 mol dm-3s-1. Calculate the rate ofdisappearance of O2
Student common mistakes:
dt
Od
dt
HCd ][
7
1][ 262
dt
HCd
dt
Od ][][
7
1 62 2
dt
HCd
dt
Od ][7
][ 62 2
)20.0(7][ 132 smoldm
dt
Od
13240.1
][ smoldmdt
Od
Differential Rate Equation Question 2:
N2(g) + 3H2(g) 2NH3(g)Suppose that at a particular moment during the reaction, molecule of hydrogen is reacting at the rate of 0.074 Ms-1. Calculate the rate of(a) formation of ammonia
(b) depletion of nitrogen
Differential Rate Equation Question 3:
4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)
The rate of disappearance of oxygen is 0.020 moldm-3s-1. Determine the rate of formation of NO and H2O and also the rate of disappearance of NH3
Differential Rate Equation Challenging Question 2:
For the reaction,
4NH3(g) + 3O2(g)→ 2N2(g) + 6H2O(g)the nitrogen gas was produced at a rate of 0.72 mol L-1 s-1.a) Write the differential rate equation for the above reaction.
b) Calculate the rate of(i) formation of water
(ii) depletion of oxygen
(iii) depletion of ammonia
Differential Rate Equation Challenging Question 3:
5Br-(aq) + BrO3-(aq) + 6H+(aq) 3Br2(aq)
+ 3H2O(g)It was found that at a particular instant bromine was being formed at the rate of 0.039 moldm-3s-1. At the instant, at what rate is(a) Water being formed
(b) Bromide ion being oxidized
(c) H+ being consumed
ANS: 0.065 mol dm-3 s-1
ANS: 0.039 mol dm-3 s-1
ANS: 0.078 mol dm-3 s-1
Differential Rate Equation Challenging Question 4:
2A + B C + 3D
It was found that at a particular instant reactant A was being disappear at the rate of 6.0 x 10-5 Ms-1. Calculate (a) The rate of reaction
(b) Rate of formation of D
(c) Rate of disapperance of B
ANS: 9.0 x 10-5 Ms-1
ANS: 3.0 x 10-5 Ms-1
ANS: 3.0 x 10-5 Ms-1
Differential Rate Equation Brain Teasers 1:
4NH3(g) + 5O2(g)→ 4NO(g) + 6H2O(g)The rate of disappearance of oxygen is 0.020 moldm-3s-1.What is the value of the k and m in the following sequence:
k,0.016,0.020,0.016,m
ANSWER:
k = 0.004 , m = 0.024
Differential Rate Equation Revision 1:
Complete the rate expression for the following reaction:
Write the rate expressions for the following reactions in terms of the disappearance of the reactants and the appearance of the products.
Differential Rate Equation Revision 2:
Differential Rate Equation Revision 3:
For the reaction A + B → 3C +D the initial rate of formation of C is 0.24 mol L-1 hr-1
a) What is the rate of disappearance of B?
b) What is the rate of formation of D?
Differential Rate Equation Revision 4:
For the reaction choose the correct phrase: R P (R-reagents, P-products)The rate of a chemical reaction is the measure of the rate at which P _________, which is equal to the rate at which the R _________. The rate of the reaction is the change in concentration over the change of time and has units of __________. For the reaction,reactant R gives product P, the rate is ________ divided by Δ of _________, where Δ means change.The rate is always___________.
Answers:is formedis consumedmol L-1 s-1-Δ [R]timepositive.