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FORM 4 CHEMISTRY QUIZ BASED ON REVISED TOPICS

Nitrogen reacts with hydrogen according to the equation below:-

N2(g) + 3H2(g)                                                             2NH3(g) DH = -92KJ

                 (a) How would the yield of ammonia be affected by increase in :-

   (i) Pressure      explain                                                                 2 marks

    (ii) temperature           explain                                                 2 marks

(b) The ammonia produced is isolated form the other gases from time to time. How does

      this  affect the equilibrium?  Explain                                  2 marks

The following is a thermochemical equation for the reaction between hydrogen and oxygen

                H2(g) + O2(g)                        H2O(l)       DH = -287kJmol-1

                Calculate the bond energy between the elements in water given that:

                O = O = +496kJmol-1        H-H = + 435kJmol-1                                          3 marks

AgClO2(s)                                        Ag(s) + ½ Cl2 (g) + O2 (g) DH = 0.00KJ/mol

                What is the effect on the position of equilibrium of the above system if temperature is

             decreased? Give a reason               2 marks

.      Bromine dissolves in water forming a brown solution, according to the dynamic

            equation below.

                                         Br2 (aq) + H2O (l)                           2H+ (aq) + Br(aq) + OBr(aq)

           State and explain the observation that could be made if a solution of sodium hydroxide

             is added to the system     2 marks

.   

 The equation below represents changes in the physical state of ions metal:                                       

            Fe(s)                                Fe(l)           DH= + 15.4kjmol-1

            Fe(l)                                      Fe(g)         DH=+354kjmol-1                                                                                                                              

         a) Calculate the amount of heat energy required to change 10kg of solid iron to gaseous iron

             Fe = 56     3 marks

Calculate the latent heat of vaporization of water

                 H2O(l)                      H2O(g)

  Given the following thermo chemical equations:-                                 H2(g) + ½O2(g)                                H2O(g) DHq= -242KJ/Mol

                                                                                                                     H2(g) + ½O2(g)                                 H2O(l) DHq= -286KJ/Mol       3 marks                                                      

 In an experiment to determine molar enthalpy of neutralization of hydrochloric acid using

             potassium hydroxide, the data below was obtained. The concentration of potassium hydroxide

            used was 0.5M

Volume of 0.5M KOH (cm3) 0 5 10 15 20 25 30 35
Total volume of acid + Base 20 25 30 35 40 45 50 55
Temperature (oC) 24 26 27 28 29 29 28 27

                (i) Plot a graph of temperature (y-axis) against volume of potassium hydroxide used     

    (ii) From your graph:

       (a) Determine the temperature change         …………………………………………………………..                                                                                                   

       (b) Find the volume of potassium hydroxide which completely neutralized 20cm3 of the acid                  

…………………………………………………..

    (iii) Calculate the heat change for the reaction (C = 4.2Jg-1K-1 density of solution = 1g/dm3)    3 marks

    (iv) Calculate the molar enthalpy of neutralization of hydrochloric acid with potassium hydroxide   2 marks

When 1.6g of ammonium nitrate were dissolved in 100cm3 of water, the temperature

             dropped by 6ºC.    Calculate its enthalpy change. (Density of water = 1g/cm3,

               specific heat   capacity is 4.2kJ kg-1K-1)

A student has been provided with sodium hydroxide solution of 2M and hydrobromic acid

           of 4M. He was asked to investigate the equation for the reaction between these two substances and

            hence determine the molar enthalpy of neutralization. He carried out the reaction and obtained the

          following    results:-

Vol. of 4M Hydrobromic acid added to 20cm3 of 2M NaOH Temperature of the mixture (oC)
4.0 26.8
6.0 30.0
8.0 33.2
10.0 36.0
12.0 35.2
14.0 34.4
20.0 30.8

(a) Draw a graph of the temperature of the mixture (vertical axis against the volume of the

                 acid added)       6 marks                                                                                                                                                                *

                 (b) Using the graph estimate the temperature of the mixture when 17cm3 of the acid was added                1 mark

                (c) Both solutions were at room temperature at the start of the experiment. Use your graph to

                      estimate the room temperature                                                                                                                         (½mk)

                (d) What is the significance of the highest temperature of the solution mixture?               1 mark *

                (e) The temperature of the mixture increased during the first additions of the acid. Why did the

                       temperature increase?          1 mark 

                                                                                                                *

(f) Suggest a reason why the temperature decreased during the latter part of the experiment  1 mark

                (g) Use your graph to determine the volume of 4M Hydrobromic acid which just neutralize

                  20cm3 of 2M NaOH                                                        1 mark                                                                                                                                 

                (h) How many moles of Hydrobromic acid are present in your answer in (g) above?         *1 mark

                (i) How many moles of NaOH are present in 20cm3 of 2M of NaOH solution 1 mark           *

                (j) Use your answers in (h) and (i) above to write an equation of the reaction taking place

                 in the  experiment. Explain clearly how you have used your answers                                      (1½mks)

                (k) Determine the molar enthalpy of neutralization of hydrobromic acid                                                                (1½mks)

15.          (a) The following results were obtained in an experiment to determine the enthalpy of solution

                  of sodium hydroxide

Mass of plastic beaker = 8.0g

Mass of plastic beaker + distilled water = 108.15g

Mass of plastic beaker + distilled water + sodium hydroxide = 114.35g

                The table below shows the temperature at fixed times after mixing

Time/seconds 0 30 60 90 120 150 180 210
Temperature ( oC) 15 21 29 28 27 26 26 25

      (i) Plot a graph of temperature (y-axis) against time (x-axis)                  6 marks                                               

      (ii) From your graph, determine the maximum temperature attained 1 mark

      (iii) Determine the temperature change of the reaction 1 mark

      (iv) Calculate the number of moles of sodium hydroxide used in the experiment    3 marks                    

           (Na = 11, H = 1, O = 16)

      (v) Use your results to determine the molar enthalpy solution of sodium hydroxide. (Density of

            solution is 1g cm-3 , specific heat capacity of solution = 4.18 KJ-1K-1)