Physical Chemistry Answers

For the reaction:
3C(s) + 4H2(g) = C3H8(g),
ΔSo = -269 J/K and ΔHo = -103.8 kJ.
Calculate the equilibrium constant at 25 oC for the reaction above.


A) 1.0
B) 3.7 x 1019
C) 1.4 x 104
D) 2.1 x 1031
E) 1.0 x 1017

assign an oxidation number to each element in the reaction co(g) +2H2(g) C3oh(g

Name 20 compounds you can find around your house

If a certain metal was irradiated by using two different light radiations of frequency x and 2x the kinetic energies of the ejected electrons are y and 3y respectively the threshold frequency of the metal will be

Elements can form compounds and molecules through

a) From experimental studies, the reaction:

A- B + C
is found to be a first-order reaction with rate constant k —— 3.6 x 10-3 s-1at T= 298 K.


i) Write down the rate law for the reaction.

ii) Calculate the half-life of the reaction at T = 298 K.

iii) The activation energy for the reaction is 46.8 kJ mol-1. Assuming that the reaction obeys the Arrhenius Equation, determine the rate constant k for the reaction at T = 320 K.
[ R= 8.314 J m )-1 K -1]
b) For a reaction of the following type:

X -- Products

the concentration of the reactant X (denoted [X]) was measured as a function of time I at T = 298 K. The measured data are as follows:

[1]

[2]



[5]



t I s
[X] / mol dm"3

0 10 60 200 500
0.500 0.351 0.145 0.0543 0.0233



Deduce the order of the reaction and determine the value of the rate constant for the reaction at T = 298 K.

a) Define all the symbols in, and briefly describe the significance of, the equation
DG=Vdp — SdT

b) Given that at 100 °C and atmospheric pressure, water is in equilibrium with steam, use the equation in part (a) to deduce that at 101 °C and atmospheric pressure, water will convert spontaneously to steam.

C) Making use of van't Hoff's equation,


deduce the shape of a graph of In K versus T"' for a reaction in which the heat capacities of reactants and products are approximately equal.

d) Using the following data for the temperature variation of the equilibrium constant for the dissociation of gaseous di-iodine to iodine atoms, obtain the standard molar enthalpy change expressed in kJ mol-1.

T I K 1274 1073 973 872
K 0.16780 0.010898 0.0018012 0.00018120

a) For a reaction of the type:
A Products

t/ s 0 20 40 60 80
[A] / mol dm-3 0.964 0.689 0.492 0.352 0.251

By drawing an appropriate graph, deduce the order of the reaction and determine the value of the rate constant for the reaction at = 298 K.

b) i) At T=350 K, the root-mean-squared speed of the molecules in a gas is crms = 558 m-1Calculate the molar mass of the gas (in units of g mol—1).

ii) At what temperature is the root-mean-squared speed of the molecules in the gas equal to twice the value at = 350 K ?

C) i) A vessel of volume 16.8 dms contains 0.164 mol of oxygen gas at a temperature of 500 °C. Assuming ideal gas behaviour, calculate the pressure inside the vessel.

ii) An amount (0.088 mol) of krypton gas is then inserted into the vessel, with the original oxygen gas still present, and the temperature is raised to 700 °C. Assuming ideal gas behaviour, calculate the total pressure inside the vessel.

5. Answer ALL parts a) — d).

The wavenumbers of the allowed rotational energy levels of a diatomic molecule are given by the equation
FJ = BJ(J+1)
a) State the factors that determine the rotational constant B for a molecule, and explain how changes in these factors would affect FJ .

b) Derive an equation for the difference in wavenumber ( ) between any two consecutive rotational energy levels.

The rotational constant for NO in the gas phase has a value of
1.705 cm 1. Calculate the wavenumber (in cm-1) of the first 4 rotational levels of NO and sketch them on an energy diagram.

d) State the specific selection rule for rotational energy level transitions for a linear molecule. Hence, draw a pure rotational spectrum for NO showing the wavenumbers of the first three transitions.

How will G vs H and G vs S diagram of Carnot cycle look like for ideal gas? How do I draw G vs T, G vs P and G vs V graphs of Carnot cycle for ideal gas?