Chem Test 4

Question 1

NH4-

NH2-

Answer 1

NH4- tetrahedral 109.5

NH2- non-linear 104.5

Question 2

Explain why boilin point of PH3 is lower than boiling point of NH3

Answer 2

PH3 has a greater atomic radius, so is less electronegative so they have weak London forces. Whereas, NH3 is more electronegative has strong H bonding between themselves

Question 3

Explain why boiling point of PH3 is lower than boiling point of AsH3

Answer 3

AsH3 has more electrons that PH3 so has stronger London forces

Question 4

[Fe3+] order

[I-] order

Answer 4

[Fe3+] is 1st order as the conc is directly proportional to the rate
[I-] is 2nd order as the conc is proportional to the square of the rate

rate= k (Fe3+][I-]^2
k= 22.5 dm6mol-2s-1

Slow Fe3+ + 2I- —> Fe2+ + I2-
Fast I2- + Fe3+ —> Fe2+ + I2

Question 5

Activation energy =

Answer 5

Ae = -R x gradient

-R= -8.314

6650

Question 6

Find pre exponential factor A

Answer 6

Shift ln of y intercept !

Question 7

[H2O2] [I-] [H+]

Answer 7

[H2O2] is 1st order as conc directly proportional to rate

[I-] is 1st order as conc is directly proportional to rate

[H+] is 0 order AS CHANGE IN CONC HAS NO EFFECT ON RATE

rate = k[H2O2][I-]
k= 0.029 dm3mol-1s-1

Question 8

The rate constant,k, for this reaction can be determined at different temperatures, T.
Explain how the student could determine the activation energy for the reaction graphically using values of k and T

Answer 8

Plot a graph of ln(k) and 1/T
Measure the gradient
Ea= -8.314 x gradient