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Form 4 Energy Changes in Chemical and Physical Processes Questions and Answers

Form 4 Energy Changes in Chemical and Physical Processes Questions and Answers. In this session, we are going to solve several exam standard questions. Answers are available in video format.

Lessons (39)

• 1.    Study the table below and answer the questions that follow. (a) Predict the heat of combustion of butane and write it on the space provided in the table above. (b) What does the sign #DeltaHc# value indicate about combustion of alkanes?
  3m 11s

• 2.    Explain why the enthalpy of neutralization of ethanoic acid with sodium hydroxide is different from that of hydrochloric acid with sodium hydroxide.
  1m 56s

• 3.    In an experiment determine the heat of combustion of methanol, #CH_3OH#, a student used a set up like the one shown in the diagram below. Volume of water=#500cm^3# Final temperature of water=#27.0^0C# Initial temperature of water=#20.0^0C# Final mass of lamp+methanol=22.11g Initial mass of lamp+methanol=22.98g Density of water=1.0g#cm^3# Specific heat capacity of water=4.2J/g/K (a)Write an
  14m 59s

• 4.    Use the information below to answer the questions that follow: (a) Define the term “enthalpy of formation” of a compound. (b) Calculate the molar enthalpy of combustion, #DeltaH4# of ethanol; #C_2H_5OH(l) +3O_2(g)to2CO_2(g)+3H_2O(l)#
  8m 44s

• 5.    Sulphur burns in air to form sulphur (IV) oxide. A simple energy level diagram for the reaction is given below. Study the diagram and answer the questions that follow. (a)What do the following represent? (i)#DeltaH_1# (ii) #DeltaH_3# (b) Write an expression, for #DeltaH_3# in terms of #DeltaH_1# and #DeltaH_2#
  3m 47s

• 6.    When 0.6g of element J were completely burnt in oxygen and all the heat evolved was used to heat #500cm^3# of water, the temperature of the water rose from #23^0C# to #32^0C#. Calculate the relative atomic mass of element J given that the specific heat capacity of water=#4.2KJ^(-1)g^-1#, density of water=#1.0gcm^-3# and molar heat of combustion of J is #380Kjmol^-1#
  6m 38s

• 7.    study the information in the table below and answer the questions below the table Calculate the enthalpy change of the reaction: #CH_4(g)+Cl_2(g) overset(U.V)(to) CH_3Cl(g)+HCl(g)#
  8m 25s

• 8.    In order to determine the molar heat of neutralization of sodium hydroxide, 100#cm^3# of 1M sodium hydroxide and 100#cm^3# of 1M hydrochloric acid both at the same initial temperature were mixed and stirred continuously with a thermometer. The temperature of the resulting solution was recorded after every 30 seconds until the highest temperature of the solution was attained. There after, the
  14m 37s

• 9.    Use the information below to answer the question that follows. Calculate the enthalpy change for the reaction CaO(s)+#CO_2#(g)#to# #CaCO_3#(s) #Ca(s)+1/2O_2(g) toCaO(s) DeltaH=-635kJmol^-1# #C(s) +O_2(s) to CO_2(s) DeltaH=-394kJmol^-1# #Ca(s)+C(s)+3/2O_2(g) to CaCO_3(s) DeltaH=-1207kJmol^-1#
  6m 48s

• 10.    Hydrogen and Flourine react according to the equation below: (a) On the grid provided below, sketch the energy level diagram for the forward reaction. (b) Calculate the molar enthalpy of formation of HF.
  2m 43s

• 11.    At 298K and 1 atmosphere, graphite changes into diamond according to the equation: C(graphite)?C(diamond);#DeltaH=2.9kJmol^-1# In the space provided, sketch a simple energy level diagram for the above change.
  2m 17s

• 12.    Hydrogen peroxide decomposes according to the equation below #H_2O_2(l)toH_2O(l)+1/2 O_2(g); DeltaH =-98kJ# 8.5 g of hydrogen peroxide contained in #100cm^3# of solution with water were completely decomposed. Determine the rise in temperature due to the reaction. (Specific heat capacity of solution=#4.2Jg^-1K^-1# density of water=#1gcm^-3# O=16 H=1)
  5m 41s

• 13.    Use the equations below to answer the questions that follow. (a) What is the name of #Delta#H1 ? (b) Calculate the heat change for the process:
  5m 24s

• 14.    (a) Distinguish between exothermic and endothermic reaction. (b) Changes of state are either exothermic or endothermic. Name a change of state that is: (i)Endothermic (ii) Exothermic (c ) When pure water is heated at 1 atmospheric pressure at sea level, the temperature of the water does not rise beyond #100^oC#,even with continued heating. Explain this observation. (d)Study the energy cycle
  6m 42s

• 15.    Use the following equations to determine the heat evolved when Aluminium metal is reacted with iron(III)oxide.
  2m 6s

• 16.    Copper (II) sulphate reacts with barium chloride according to the equation below. #CuSO(aq)+BaCl_2(aq)toCuCl_2(aq)+BaSO_4(s) ; DeltaH =-17.7 kJmol^-1# Calculate the temperature change when #900cm^3# of 1M copper (II) sulphate were added to 600#cm^3# of 1M barium(II)chloride.(Assume heat capacity of solution is #4.2Jg^-1K^-1# and density is 1g#cm^-3#)
  7m 14s

• 17.    Below is a sketch of a reaction profile. (a) On the diagram, show the heat of reaction, #Delta#H. (b) State and explain the type of reaction represented by the profile.
  1m 35s

• 18.    Methane reacts with oxygen according to the equation below. #CH_4(g)+2O_2(g)toCO_2(g)+2H_2O(l); DeltaH=-890 kJmol^-1# Calculate the volume of methane which would produce 111.25 kJ when completely burnt. (Molar volume of a gas=24 litres)
  3m 16s

• 19.    The scheme below shows the energy changes that are involved between ice,water and steam. Study it and answer the questions that follow. (a) What name is given to the energy change, #Delta#H4 (b) What is the sign of #Delta#H3? Give a reason.
  2m 0s

• 20.    Study the diagram below and answer the questions that follow. (a)What do #Delta#H1 and #Delta#H2 represent? (b) Write an expression to show the relationship between #Delta#H1, #Delta#H2 and #Delta#Hc3.
  3m 4s

• 21.    The thermochemical equations for the formation of hydrogen peroxide under standard conditions are: Write the thermochemical equation for the molar heat of vaporization of hydrogen peroxide.
  2m 2s

• 22.    (a) State two factors that should be considered when choosing fuel for cooking. (b) The diagram below represents a set-up that was used to determine the molar heat of combustion of ethanol. During the experiment, the data given below was recorded. Volume of water=#450cm^3# Initial temperature of water=#25^0C# Final temperature of water=#46.5^0C# Mass of ethanol+lamp before burning=125.5g Mass of
  11m 28s

• 23.    (a) Define the standard enthalpy of formation of a substance. (b) Use the thermo chemical equations below to answer the questions that follow. (i) Name two types of heat changes represented by #Delta#H3 (ii) Draw an energy level diagram for the reaction represented by equation 1. (iii) Calculate the standard enthalpy of formation of ethane. (iv) When a sample of ethane was burnt, the heat produced
  15m 51s

• 24.    (a) What is meant by molar heat of solution? (b) The lattice energy of sodium bromide and hydration energies of sodium and bromide ions are: 733,406 and 335 #kJmol^-1# respectively. (i) Complete the energy cycle diagram below by inserting the values of #Delta#H1, #Delta#H2 and #Delta#H3 (ii) Determine the molar heat of solution of solid sodium bromide.
  3m 5s

• 25.    The energy level diagram below shows the effect of a catalyst on the reaction path. (a) What does point M represent? (b) With reference to energy level diagram, explain how a catalyst speeds up the rate of a reaction.
  1m 45s

• 26.    (a) In the flow chart below, some processes have been identified and others labelled. Study it and answer the questions that follow. (i) Give the names of the processes: I.H II.G (ii) Name one substance that can undergo process F when left in an open container in the laboratory. (iii) The process J is called deposition. Using water as an example, write an equation that represents the process of
  8m 34s

• 27.    What is the name given to each of the following: a)Ability of a metal to be made into wire b)Minimum energy required for a chemical reaction to start. c)type of force that holds atoms of neon.
  1m 14s

• 28.    A beaker contained 75.0 #cm^3# of aqueous copper(II)sulphate at #23.70^C.# when scrap iron metal was added to the solution, the temperature rose to #29.3^0C#. a) Write an ionic equation for the reaction that took place. b) Given that the mass of copper deposited was 5.83g, calculate the molar enthalpy change in kJmol-1.(specific heat capacity of solution=#4.2Jg^-1K^-1#,density of solution=#1.0gcm
  5m 47s

• 29.    a) 50#cm^3# of 1M copper(II)sulphate solution was placed in a 100#cm^3# plastic beaker. The temperature of the solution was measured. Excess metal A powder was added to the solution, the mixture stirred, and maximum temperature of the mixture measured . the results obtained are given in the table below. i)arrange the metals A, B, C and copper in order of reactivity starting with the least
  8m 11s

• 30.    The thermal chemical reaction between carbon and sulphur is as shown by the equation below: #C(s)+2S(s)toCS_2(l) Delta=+117.0 kJmol^-1# On the grid below, sketch and label the energy level diagram for the reaction.
  1m 46s

• 31.    (a) What is meant by molar heat of combustion? (b) State the Hess’s Law. (c) Use the following standard enthalpies of combustion of graphite, hydrogen and enthalpy of formation of propane. (i) Write the equation for the formation of propane. (ii) Draw an energy cycle diagram that links the heat of formation of propane with its heat of combustion and the heats of combustion of graphite and hydrogen
  5m 17s

• 32.    Hydrazine gas, burns in oxygen to form nitrogen gas and steam. (a) Write an equation for the reaction. (b) Using the bond energies given below. Calculate the enthalpy change for the reaction in (a) above.
  3m 56s

• 33.    A student investigated the effect of an electric current by passing it through some substances. (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.
  1m 16s

• 34.    When 20 #cm^3# of l M sodium hydroxide was mixed with 20 #cm^3# of 1 M hydrochloric acid, the temperature rose by #6.7^0C#. Assuming the density of the solution is l g/#cm^3#and the specific heat capacity of the solution is 4.2 #Jg^-1k^-1#; (a) Calculate the molar heat of neutralization; (b) When the experiment was repeated with 1 M ethanoic acid, the temperature change was found to be lower than
  2m 42s

• 35.    (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?
  0m 33s

• 36.    The figure below shows an energy cycle. (a) Give the name of the enthalpy change AI-II. (b) Determine the value of #H_3#.
  1m 39s

• 37.    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
  1m 9s

• 38.    (a) Define molar heat of displacement. (b) The following ionic equation represents the reaction between metal Y and an aqueous solution of #Z^(2+)(aq)+ Y(s) to Z(s) + Y_2 (aq)#; AH = -ve Draw an energy level diagram to represent the reaction.
  1m 53s

• 39.    The heat of solution and hydration energy of potassium chloride is 17.2 kJ and -689 kJ respectively. Calculate the lattice energy of potassium chloride.
  1m 52s