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​These are chemistry questions and answers categorized according to topics, papers i.e. Paper 1 and 2, Levels i.e. form 1 to form 4, kcse year the examination was done and section A or B
Select topic/category to open topical questions from that particular option provided. ​Chemistry Topics
(a) Define molar heat of displacement.
(b)The following ionic equation represents the reaction between metal Y and an aqueous solution of Z2+. 
Draw an energy level diagram to represent the reaction
ANSWERS
In the Haber process, nitrogen reacts with hydrogen according to the following equation.
(a)What would be the effect of adding a catalyst on the position of the equilibrium?
(b) Explain why it is not advisable to use temperatures higher than 773 K in the Haber process.
ANSWERS
(a)No effect/does not affect the position of the equilibrium.
(b)Forward reaction is exothermic, excessive temperatures would favour the backward reaction therefore lowering the yield of ammonia.
The following procedure was used to investigate the temperature changes that occur when sodium hydroxide solution is added to dilute hydrochloric acid.
(i) Place the acid in a glass beaker and record its temperature. (ii) Add a known volume of sodium hydroxide solution. (iii) Stir the mixture and record the highest temperature reached. (iv) Repeat steps (ii) and (iii) with different volumes of sodium hydroxide solution. (a) State two factors that must be kept constant in this experiment (b) Explain how the use of a polystyrene cup will affect the results.
ANSWERS
(a) State one characteristic of a reaction where equilibrium has been attained.
ANSWERS
(a) What ¡s meant by molar heat of neutralisation? (1 mark)
(b) In an experiment to determine the molar heat of neutralisation, 50 cm3 of 1M hydrochloric acid was neutralised by adding 10 cm3 portions of dilute sodium hydroxide. During the experiment, the data in Table 1 was obtained. 
(iii) Determine from the graph the: I. volume of sodium hydroxide which completely neutralises 50 cm3 of 1M hydrochloric acid. (1 mark) II. change in temperature,△T, when complete neutralisation occurred. (1 mark) (iv) Calculate: I. the heat change, △H when complete neutralisation occurred. (Specific heat capacity = 4.2 Jg-1K-1, density of solution 1.0 gcm-3) (2 marks) II. molar heat of neutralisation of hydrochloric acid with sodium hydroxide. (1 mark) (v) How would the value of molar heat differ if 50 cm3 of 1M ethanoic acid was used instead of 1M hydrochloric acid? Give a reason. (2 marks)
Expected Response
The figure below shows an energy cycle.
(a)Give the name of the enthalpy change ΔH1.
(b)Determine the value of ΔH3.
ANSWERS
Enthalpy of formation of hydrogen peroxide or enthalpy of formation
The heat of solution and hydration energy of potassium chloride is —17.2kJ and —689kJ respectively. Calculate the lattice energy of potassium chloride. (2 marks)
Expected Response
The graph in Figure 4 was obtained when a certain substance was heated and its temperature recorded at regular intervals.
(a) State the purity of the substance. (I mark)
(b) Explain the answer in (a). (2 marks)
Expected Response
(a) What is meant by lattice energy?
b) Study the energy level diagram below and answer the question that follows 
What type of reaction is represented by the diagram?
ANSWERS
(a) Enthalpy change, when one mole of crystal lattice is broken into its ions in gaseous state.
(b) Endothermic reaction (process)
When 20cm3 of 1 M sodium hydroxide was mixed with 20cm3 of 1 M hydrochloric acid, the temperature rose by 6.70C Assuming the density of the solution is 1 g/cm3 and the specific heat capacity of the solution is 4.2Jg-1k-1.
(a) Calculate the molar heat of neutralization; (b) When the experiment was repeated with 1 M ethanoic acid, the temperature changes was found to be lower than that with 1 M hydrochloric acid. Explain.
ANSWERS
(b)Some energy is used to ionise the weak acid first before it can neutralize. So not all energy is used in neutralization.
Hydrogen peroxide decomposes according to the equation below:
8.5 gm of hydrogen peroxide contained in 100cm3 of solution with water were completely decomposed. Determine the rise in temperature due to the reaction. Specific density of water = 1g/cm3 O =16, H = 1,).
Expected Response
(a) (i) what is meant by the term Enthalpy of formation?
(ii) The enthalpies of combustion of carbon, methane and hydrogen are indicated below: 
(i) Draw an energy cycle diagram that links the enthalpy of formation of methane to enthalpies of combustion of carbon, hydrogen and methane
(ii) Determine the enthalpy of formation of methane (b) An experiment was carried out where different volumes of dilute hydrochloric acid and aqueous sodium hydroxide both at 25°C were mixed and stirred with a thermometer. The highest temperature reached by each mixture was recorded in the table below 
(i) On the grid provided. plot a graph of highest temperature (vertical axis) against volume of hydrochloric acid ( horizontal axis)
(ii) Using your graph , determine the (a) Highest temperature reached (b) Volume of acid and base reacting when highest temperature is reached
(iii) Calculate the amount of heat liberated during the neutralization process .(specify heat capacity is 4.2 j g -1 k-1 and the density of solution is 1.0 g cm-3)
(c) The molar enthalpy of neutralization between hydrochloric acid and ammonia solution was found to be -52.2 kJ mol-1, while that of hydrochloric acid and sodium hydroxide was – 57.1 Kj mol-1. Explain the difference in these values.
ANSWERS
(a)(i)This is the heat absorbed or evolved when one mole of any substance is formed from its constituent elements in their normal states.
(c)The molar heat of neutralisation between a strong acid and a weak base is low because some of the heat is used to ionise (1) the weak base before neutralization.
For strong acid and strong base they are completely ionised.
A student investigated a property of acids M and N by reacting equal volumes of acid M and N of the same concentration with equal volumes of 2M potassium hydroxide.
The results were recorded in the table below. 
a) Which of the acids is likely to be a weak acid? Explain.
b) Write the equation for the reaction between ethanoic acid and potassium hydroxide.
ANSWERS
a) Write an equation for the reaction
b) Using the bond energies given below, calculate the enthalpy change for the reaction in (a) above 
ANSWERS
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December 2024
AuthorMaurice Atika is a teacher and a netprenuer. |
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