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EQUILIBRIUM

QUESTION 1

(a)  Describe dynamic equilibrium.

(b)  Nitrosly chloride, NOCl decomposes into nitrogen monoxide, NO,  and chlorine gas, Cl2. The Kc for the reaction is 0.00350.

(i)     Write balance equilibrium reaction equation for the reaction.

(ii)    Write the Kc expression.

(iii)   The initial concentration of NOCl, NO and Cl2 in the reaction vessel are 0.0120M, 0.00280 M and 0.00230 M respectively. Determine the direction of reaction in order to reach equilibrium.

(iv)   Calculate the concentration of NO at equilibrium.

 

QUESTION 2

Give Kp at 400 °C for the following equilibrium, NH4Cl(s)   =  NH3(g)   +   HCl(g)   Kp = 32

Calculate Kc.

 

QUESTION 3

A vessel contains 0.0015 M hydrogen gas, H2,  0.0018 M bromine gas, Br2 and 0.035 M HBr gas is allowed to reach equilibrium at 480 °C. The concentration of HBr at equilibrium is 0.0225 M. Calculate the concentration of H2 and Br2 at equilibrium.

 

THERMOCHEMISTRY

QUESTION 1

A 18.0 g 0f tridecane, C13H28 is burned in bomb calorimeter containing 1200 g water at an initial temperature of 25.0 C. After the combustion, the final temperature is 39.5 C. Calculate the enthalpy of combustion of tridecane in kJ/mol [ Heat capacity of bom calorimeter (exclude water) = 837 J/C; specific heat capacity of water = 4.184 J/g.C; molar mass of tridecane = 184.41 g/mol]

QUESTION 2

(a) Define standard enthalpy change of combustion,

(b) Give standard enthalpy change formation of C8H18(g), H2O(l) and CO2(g) are -250 kJ/mol, -286 kJ/mol and -394 kJ/mol respectively. Calculate the enthalpy change of combustion of octane, C8H18 by using an algebraic method.

(c) Draw the energy cycle for (b) above.

QUESTION 3

(a) Given the following data;

Electron affinity of chlorine:  -349 kJ/mol

Enthalpy of atomization of barium: +180 kJ/mol

Enthalpy of atomization of chlorine: +122 kJ/mol

Enthalpy of formation of barium chloride: -859 kJ/mol

First and second ionization energy of barium: +1468 kJ/mol

(i)   Draw Borh-Haber cycle of barium chloride.

(ii)  Calculate the lattice enthalpy of Barium chloride, BaCl2.

(iii) Predict whether lattice enthalpy of BaCl2 is larger or smaller than lattice enthalpy of CsCl. Explain.

QUESTION 4

Given the following data:

Lattice enthalpy of magnesium chloride 2526 kJ/mol. 

Standard enthalpy of hydration of Mg2+(g) and Cl-(g) are -1923 kj/mol and -338 kj/mol repectively.

Calculate the enthalpy change of solution of MgCl2.

PART II

QUESTION 7

(a)     Consider the following reaction;

2 HgCl2  +  C2O4 2-   →   2 Cl   +  2 CO2    +   Hg2Cl2

The data below obtained from the reaction above by measuring the number of moles of Hg2Cl2 that precipitate per liter per minute.

Experiment [HgCl2], M [C2O4]2-, M Initial rate

Mol/L.min

1

2

3

4

0.105

0.105

0.052

0.052

0.15

0.30

0.30

0.15

1.8 X 10-5

7.1 X 10-5

3.5 X 10-5

8.9 X 10-6

(i)    Calculate the order of reaction with respect to HgCl2 and C2O4 2- .

(ii)    What is the value of the rate constant k?

(iii)    What would be the initial rate of reaction if [HgCl2] = 0.157 M and [C2O4 2- ] = 0.25 M?

(b)    The rate constant for decomposition of HI at 700 K is k = 0.0012 L/mol.s .

(i)  If initial concentration of HI is 0.800 M, what will [HI] be at t = 1 hour?

(ii)  At what time will [HI] = 0.350 M for the reaction?

(c)    Explain 3 factors that affect the rate of reaction.

PART II

QUESTION 5

(a)    Give two different between ionic bonding and covalent bonding.

(b)    Consider the compound Calcium chloride, CaCl2. Use Lewis electron dot to describe the formation of chemical bond in the CaCl2.

(c)     Consider the following covalent bond:

C-O,  C-F, C-S , C-Br

(i)    Arrange covalent bond in order of increasing bond length.

(ii)    State bond that has highest bond energy, explain.

(d)   Use formal charge to Draw the best Lewis structures for ClO3.

(e)    Draw resonance structures of SO3.

(f)     Draw and name the molecular shape for BrF3.

(g)    Consider molecule H2C=O;

(i)     Draw the orbital overlapping in H2C=O

(ii)    Identify sigma and pi bonds in H2C=O

PART II

QUESTION 4

(a)    Cu is a transition element,

(i)    Write the ground state electronic configuration for Cu.

(ii)   How many inner electron in Cu at ground state?

(b)   Given the following species:

S2-, Cl, K+, Ca2+

(i)    Arrange the elements in order of increasing ionic size.

(ii)   Explain answer in b(i) above.

(c)     Explain the first ionization energy of fluorine atom.

(d)     Give two factor that influence the first ionization energy.

(e)     An element G has the following successive ionization energies

IE1 IE2 IE3 IE4 IE5 IE6 IE7 IE8
900 2300 3600 8560 9500 11600 13600 16000

(i)    Write the general valence electronic configuration for G.

(ii)    Explain answer in e(i) above.

(iii)   If elemen G is in period 3, state the group number and name of element.

PART II

QUESTION 3

(a)      Consider the following reaction;

Zn (s)   +   H2SO4 (aq)   →    ZnSO4 (aq)   +    H2 (g)

In experiment 201 mL hydrogen gas is collected over water at 27 oC and a barometric pressure of 733 torr. The vapor pressure of water at 27 oC is 26.74 torr. How many grams of hydrogen gas are produce? [R = 0.0821 L atm/mol. K]

(b)    At 298 K, a sealed 750 mL vessel contains equimolar amount of oxygen, hydrogen and helium gases at total pressure of 2.85 atm.

(i)     What is the partial pressure of the hydrogen gas?

(ii)     Predict whether the of the partial pressure of the hydrogen gas increases, decreases or remain the same if neon gas is added into the vessel.

(c)    List the five basic postulates of the kinetic molecular theory. Which assumption is incorrect at very high pressure? Which one is incorrect at low temperature?

(d)    An ideal gas was contained in a glass vessel of unknown volume with a pressure of 0.960 atm. Some of the gas was withdrawn from the vessel and used to fill a 25.0 mL glass bulb to a pressure 1.00 atm. The pressure of the gas remaining in the vessel of unknown volume was 0.882 atm. All the measurements were done at the same temperature. What is the volume of the vessel?

PART II

QUESTION 2

(a)   Given the half reaction equation:

Cr2O7 2-  (aq)   →   Cr3+(aq)   (basic solution)

(i)    Balance the half equation above.

(ii)    State whether oxidation or reduction process is involved.

(b)    A 25.00 mL sample of HNO3 was added to 0.200 g sample of Ba(OH)2. All the Ba(OH)2 reacted, leaving some excess of HNO3.

2HNO3 (aq)  +   Ba(OH)2 (aq)   →  Ba(NO3)2  (aq)  +   2 H2O (l)    (Reaction 1)

The excess HNO3 from first reaction above required 25.00 mL of 0.015 M KOH to complete the following reaction.

HNO3 (aq)  +   KOH (aq)   →  KNO3 (aq)  +   H2O (l)      (Reaction 2)

(i)    Calculate the number of mole of the original HNO

(ii)    Calculate the molarity of the original HNO3.

(iii)    State the mass (g) of KNO3

(c)    Calculate the volume (L) of 2.50 M  Ba(OH)2  that contains 2.50 mol of hydroxide ion, OH.