1. From description From Data From a graph
Calculating rxn rates
From description
From Data
From a graph

2. Please write From description Ex 1
A bottle of wine contains ~72.0 g of ethyl alcohol, C2H5OH. When left open, the ethyl alcohol changes into acetic acid (vinegar)
C2H5OH + O2  CH3COOH + H2O
The wine changed completely into vinegar after 60 days.
What is the average reaction rate(mol/d), of this transformation?

3. Please check 1. Calculate # of moles of alcohol.
1𝑚𝑜𝑙C2H5OH 𝑥 = 46.08𝑔 72.0𝑔
x = 1.56 mol of C2H5OH
2. Calculate the average rate:
Rate =
Rate = 1.56 / 60
Rate = mol/day
2.60x10-2mol/day

4. From description
Ex 2
Below is a balanced equation:
A + B  C + 2D
A student dissolved 0.15 mol of substance A in solution B. After a 10 minutes, 0.05 mol of A is left.
What is the average rate of formation of D in mol/sec?

5. 1. Calculate moles of A used in 10 min: 0.15 – 0.05 mol = 0.10 mol A
Rxn: A + B  C + 2D
1. Calculate moles of A used in 10 min:
0.15 – 0.05 mol = 0.10 mol A
2. Calculate the moles of D produced:
moles of D produced = 0.20 mol
3. Calculate the rxn time in sec:
time = 10 x 60 =600 sec
Rate =
4. Calculate the average rate:
Rate = 0.20 / 600
Rate =3.3 x 10-4 mol/sec

6. Please write From data Ex 1
The combustion of a candle is recorded below.
Before combustion
After combustion
Mass of candle (g)
165.5
162.0
Time (h:min)
1:00
6:00
Molar mass
C25H52 = g/mol
C25H O2  25 CO H2O
Calculate the average rate of rxn in mol/h.

7. Please write 1. Calculate the # moles burned: 165.5 – 162.0 = 3.5 g
1𝑚𝑜𝑙C25H52 𝑥 = 𝑔 3.5𝑔
x = mol of candle burned
2. Calculate the average rate:
Rate =
Rate = / 5
Rate = mol/hr are burned
2.0 x 10-3 mol/hr

8. Please write From data A + B  C
1. # mol C after 3s =
0.25 mol
2. Average rate of C formation:
Rate =
Rate = 0.25 / 3
Rate = mol/s of C
Find the average rate for the formation of C during the first three seconds?

9. Ex 2
Mg + 2HCl  H2 + MgCl2. The following table shows the volume of H2 formed during the reaction as a function of time.
Time (s)
Volume of H2 (mL) 10 50
100
150 8 32 45
What is the average rate of formation of H2 between the 25th and 75th second?
Vol of H2 = 39mL – 19mL
Rate =
= 20 50
= 0.40mL/s
= 20 mL

10. Average vs Instantaneous Rates
Please write
Average vs Instantaneous Rates
Average rate is found by picking two points in time and calculating the slope of the secant between them.
Instantaneous rate is found by picking one point, and drawing a tangent. The slope of the tangent is then calculated. Δt
tangent ΔA
Amount
secant ΔA
Instantaneous Δt
Average 2 4 7
Time

11. Rate equation for complex rxns:
Please write
Rate equation for complex rxns:
Rxns that proceed in multiple steps don’t always follow the predicted rate equation!
Why?
Because there are multiple activated complexes. The rate limiting step will have the greatest effect on the rate.
The rate equation is determined experimentally
A + 2B  C predicted rate=k[A][B]2
Let’s check according to experimental data!

12. Please write [A] [B] Rate (mol/Ls) 1 0.100 M 0.600 M 3.30 x 10-5 2
A + 2B  C rate=k[A]x[B]y
Experiment
[A]
[B]
Rate (mol/Ls) 1
0.100 M
0.600 M
3.30 x 10-5 2
0.300 M
1.65 x 10-5 3
5.50 x 10-6 4
0.200 M
2.20 x 10-5

13. Please write = = Compare exp 1 & 2
𝒓𝒂𝒕𝒆 𝟏=𝒌 𝑨 𝒙 𝑩 𝒚 𝒓𝒂𝒕𝒆 𝟐=𝒌 𝑨 𝒙 𝑩 𝒚 𝟑.𝟑𝟎× 𝟏𝟎 −𝟓 =𝒌 𝟎.𝟏𝟎𝟎 𝒙 𝟎.𝟔𝟎𝟎 𝒚 𝟏.𝟔𝟓× 𝟏𝟎 −𝟓 =𝒌 𝟎.𝟏𝟎𝟎 𝒙 𝟎.𝟑𝟎𝟎 𝒚 𝟐= 𝟎.𝟔𝟎𝟎 𝟎.𝟑𝟎𝟎 𝒚 𝟐= 𝟐 𝒚 𝒚=𝟏 =

14. Please write = = Compare exp 3 & 4 𝒓𝒂𝒕𝒆 𝟒=𝒌 𝑨 𝒙 𝑩 𝒚 𝒓𝒂𝒕𝒆 𝟑=𝒌 𝑨 𝒙 𝑩 𝒚
𝒓𝒂𝒕𝒆 𝟒=𝒌 𝑨 𝒙 𝑩 𝒚 𝒓𝒂𝒕𝒆 𝟑=𝒌 𝑨 𝒙 𝑩 𝒚
𝟐.𝟐𝟎× 𝟏𝟎 −𝟓 =𝒌 𝟎.𝟐𝟎𝟎 𝒙 𝟎.𝟏𝟎𝟎 𝒚 𝟓.𝟓𝟎× 𝟏𝟎 −𝟔 =𝒌 𝟎.𝟏𝟎𝟎 𝒙 𝟎.𝟏𝟎𝟎 𝒚
𝟒= 𝟎.𝟐𝟎𝟎 𝟎.𝟏𝟎𝟎 𝒙
𝟒= 𝟐 𝒙
𝒙=𝟐 =

15. Please write A + 2B  C rate=k[A]2[B]
Solve for k : rate=k[A]2[B] 3.30 x 10-5mol/Ls = k (0.100 mol/L)2(0.600 mol/L) 3.30 x 10-5mol/Ls = k (6.00 x 10-3 mol3/L3) k=5.50 x 10-3 𝑚𝑜𝑙 𝐿𝑠 𝑚𝑜𝑙 3 𝐿 3 k=5.50 x 10-3 𝑚𝑜𝑙 𝐿𝑠 × 𝐿 3 𝑚𝑜𝑙 3 k= 5.50 x 10-3 𝐿 2 𝑚𝑜𝑙 2 𝑠

16. Predicting Rates of Reactions:
Reactions that have reactants:
1. With oppositely charged ions are very fast
2. With few or weak bonds are faster than those with many or strong bonds
Ag+ + Cl-  AgCl
Faster
Mg + HCl  MgCl + H2
C2H5OH + 3O2  2CO2 + 3H2O

17. Faster Faster 3. Gases > aqueous/liquids > solids
One step is faster than multiple
(unless a catalyst is being used!)
Faster
H2 (g) + F2 (g)  2HF (g)
Mg (s) + 2H2O (l)  2Mg2+ (aq) + 2OH- (aq) + H2 (g)
4NH3 (g) + 7O2 (g)  4NO2 (g) + 6H2O (g)
Faster
2H2 (g) + O2 (g)  2H2O (g)

18. Predicting rxn rates:
Primary effect on rxn rate (for a particular rxn!)
Temperature
Concentration
Surface area
Nature of material
Catalyst

19. Please write Predicting rxn rates: Reactants that
Fastest of all due to static attraction!
Reactants that
are have oppositely charged ions
Gases > aqueous/liquids > solids
with few or weak bonds (ionic bonds are weaker than covalent)
Bi-molecular collisions are faster than multi- molecular collisions

20. Fastest --> Slowest
Rank the following from fastest to slowest. 1.
H2 (g) + F2 (g)  2HF(g)
Ag+(aq) + Cl-(aq)  AgCl(aq) 2. 3.
C2H5OH(aq) + 3O2(g)  2CO2(g) + 3H2O(l)
Fastest --> Slowest 2 1 3

21. 4NH3 (g) + 7O2 (g)  4NO2 (g) + 6H2O (g)
Which would have the greatest rate? A.
Hg (l) + Br2 (g)  HgBr2 (s) B.
2H2 (g) + O2 (g)  2H2O (g) C.
Ag+ (aq) + Cl- (aq)  AgCl (s) D.
4NH3 (g) + 7O2 (g)  4NO2 (g) + 6H2O (g) C

22. Hand in Homework & do Textbook practice3
5 tricky (must use gas law also)
P225 4