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# OCR Chemistry F322~ 4th June 2013~ AS Chemistry watch

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Hard A= 72
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Very Easy A=82
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1. Please help I don't get this question !!!!!! I do understand enthalpy formation using hes's law but this some how has equations !! please clear the air for me i dont want confusion to take over cheers
2. (Original post by rollinglikerob)
Q=mcDeltaT is the absorbed by or lost from the surroundings. Temperature has been lost, so -10 in the equation, gives you a negative value, so the energy absorbed by or lost from the chemical system is simply Q with the opposite sign. From there you can work out the enthalpy change per mole
...

Why even bother changing the sign in the first place then..? The way I was taught was to have Q positive and then fix the sign at the end.
3. (Original post by hosamthemaster)
Please help I don't get this question !!!!!! I do understand enthalpy formation using hes's law but this some how has equations !! please clear the air for me i dont want confusion to take over cheers
You can form a cycle, since the second equation gives the enthalpy change of formation of CO...
4. (Original post by GeneralOJB)
...

Why even bother changing the sign in the first place then..? The way I was taught was to have Q positive and then fix the sign at the end.
That's the theory behind it how I've been taught it, just so you don't mess up and put the wrong charge. Q is the enthalpy change in terms of surroundings, so if the temperature of the surroundings has risen, then Q is positive, if temperature has fallen - Q is negative. And then the opposite for the reaction.

Anyway I'm off to college now, will be back when I'm there. Apologies if I'm still confusing you, I'm a bit all over the place today
5. So if I create a cycle that leaves me with B+A=C therefore

-111+A=-193

-82 is that right
6. If the reaction gives out heat(raises temperature) it is -X
If the reaction take in heat(decreases temperature) it is +X
That's right isn't it?
7. Am I overcomplicating my head by doing legacy papers? They are so hard!
8. (Original post by hosamthemaster)
Please help I don't get this question !!!!!! I do understand enthalpy formation using hes's law but this some how has equations !! please clear the air for me i dont want confusion to take over cheers
-111--193-=+82
9. (Original post by hosamthemaster)
So if I create a cycle that leaves me with B+A=C therefore

-111+A=-193

-82 is that right
I get that its +82... draw two arrows, one going to the left hand side (of the first equation) and one going to the right... The one going to the right has a value of -111, the one going to the left is what you want to find.
10. Some useful questions from legacy papers

Why do bond enthalpies have negative values?
 Because bond breaking is endothermic
What are the standard conditions?
 298K; 100KPa
State manufacturing process in which hydrogen is used
 Haber process (100atm, 300 degrees)
 Production of margarine
What is meant by exothermic?
 A reaction that releases energy
 Has a negative ΔH
Define the term bond enthalpy
 Energy needed to break one mole of bonds
 In the substance in a gaseous state
Suggest why standard enthalpy change is different from the one calculated from average bond enthalpies?
 Actual bond enthalpies may be different from average values
 Conditions aren’t standard
Suggest why experimental enthalpy change of combustion is different than actual enthalpy change?
 May have been incomplete combustion
 Some heat is lost to the surroundings
Write an equation including state symbols, for the bond enthalpy of I־I
 I – I (g) → 2I (g)
Compare the sustainability of fermentation and hydration in terms of a) availability of starting materials b) energy requirements c) atom economy
Availability
 Sugar renewable because obtained from plants
 Ethane finite because obtained from crude oil
Energy requirements
 Fermentation: energy needed for distillation
 Hydration: energy needed to produce steam
Atom economy
 AE of hydration is 100% which is higher than fermentation’s 51%
 In fermentation, co2 is produced
 In hydration, ethanol is only product
 Improve AE of fermentation by finding a use for CO2
Cis-trans isomerism
 C=C bond restricts rotation
 Each C on C=C is attached to different groups
 Restricted rotation traps the group on one side of double bond
 Give examples
Describe with the aid of suitable diagram, the formation of pi-bond in propene. State the shape and bond angle around each carbon atom [6]
 Pi-bond is formed by sideways overlap of p-orbitals
 Diagram

Why do both cis and trans isomer produce same structural isomer?
 Because C=C restricts rotation
 Product is saturated so no restricted rotation
Outline the processes of how components obtained from fractional distillation are refined with aid of suitable equations. State the importance of products formed in each process [8]
 Cracking: C10H22  C8H18 + C2H4
 Isomerisation: 

 Reforming:  +H2
 The processed products are:
 Used in fuel
 As they are better fuels as they have lower boiling point
 Alkenes from cracking are used in polymer synthesis
 H2 used in Haber Process
Cyclohexene is converted into cyclohexane. What are the reagents and conditions?
 Reagent: H2
 Condition: nickel catalyst
State a suitable reagent for dehydrating alcohol
 H2SO4
Outline how alkenes are used in manufacturing margarine
 Unsaturated oils
 Are hydrogenated
 In presence of nickel catalyst
Outline how alkenes are used in making polymers
 Ziegler-natta catalyst
Difficulty in disposing polymers
 Produce toxic fumes when burnt
 If contains Cl, Cl radicals are also evolved when burnt
Ways to treat waste polymers
 Use as chemical feedstock
 Sorting and recycling
 Cracking to produce organic molecules
 Use gas scrubbers to reduce fumes
What are homologous series?
 Same functional group
 Each successive member differing by CH2
Converting propanol to bromopropane
 Reagent: NaBr/H2SO4
 Condition: heat/reflux
Bromopropane elimination reaction with OH ions makes

Condition required: ethanol
 CH4 + Br2 → CH3Br + HBr
Outline how ethanol is produced industrially from sugars and from ethene. Comment on the decisions that a company needs to consider when deciding which of these methods to use.
sugars
 use of yeast/fermentation ¸
 equation: C6H12O6 → 2C2H5OH + 2CO2
 importance of absence of air/anaerobic conditions
 distil to obtain ethanol
ethene
 use of steam¸with phosphoric acid catalyst
 equation: C2H4 + H2O →C2H5OH ¸
issues for consideration
 availability of raw materials/oil countries use ethene/warm with no oil can grow sugar: use sugar¸
 cost of energy/ethene requires energy but sugars does not¸
 consideration of pollution/effect on the environment¸
What is activation energy?
 Minimum energy required for a reaction to occur
Ammonia, NH3 is made industrially by the Haber process. State the raw materials used to supply the nitrogen and hydrogen for the Haber Process.
 nitrogen: air
 hydrogen: methane/water
In the conditions often used in the Haber process, there is only a 15% yield of ammonia. Suggest what happens to any unreacted nitrogen and hydrogen.
 Recycled
How does nitric acid behave as an acid?
 Proton donor
Construct an equation for the acid-base reaction of ammonia with nitric acid.
 NH3 + HNO3 → NH4NO3
Describe, using one example in each case, the different modes of action of homogeneous and heterogeneous catalysis. [10]
 homogeneous: catalyst in same phase as reactants ¸;
 heterogeneous: catalyst in different phase as reactants ¸
 homogeneous: any example, e.g. Cl in ozone breakdown ¸
 mode of action to match example: forms a intermediate/ClO ¸
 propagation stages shown ¸
 overall equation ¸
 heterogeneous: any example, e.g. Fe in Haber process ¸
 mode of action to match example: reactants adsorbed on surface of catalyst ¸
 weakens bonds in reactants ¸
 reaction takes place and products diffuse from surface of catalyst ¸
Outline why the use of catalysts provides economic benefits to this industry [4]
 reaction proceeds quicker ¸
 lower temperature ¸
 energy costs saved ¸
 more products can be made and therefore more sold ¸
 enable reactions to take place that would be impossible otherwise ¸
Explain the greenhouse effect [3]
 uv from the sun ¸
 released form earth’s surface as i.r. ¸
 i.r. absorbed by molecules of greenhouse gases ¸
Why is carbon dioxide considered to make a significant contribution to the greenhouse effect?
 considerable amounts of greenhouse gases are released by burning fossil fuels
Approximately 79% of the atmosphere consist of nitrogen. Explain why this does not contribute to the greenhouse effect.
 no i.r. active vibrations ¸because no charge on dipole
Describe the structure of a catalytic converter.
 transition metals ¸
 Pt/ Pd/ Rh ¸
 honeycomb structure for maximum surface area
Explain how the design of a catalytic converter allows both carbon monoxide and nitrogen monoxide to be removed.
 oxidation of CO (and unburned hydrocarbons) to CO2 ¸
 reduction of NO to N2 ¸
 2NO(g) + 2CO(g)→N2(g) + 2CO2(g) ¸
 Pd and Pt promote oxidation
 Rh promotes reduction
State le chatelier’s princicle
 when the conditions on a reaction in equilibrium are changed
 the (equilibrium) moves in the direction to minimise the effects of the change
Describe and explain why these conditions are a compromise between rate and equilibrium.
rate
 (increased) pressure increases rate because molecules are closer together/ more concentrated
 (increased) temperature increases rate because molecules are moving faster/ have more energy
equilibrium
 increased pressure pushes equilibrium to RHS; because
 fewer (gas) moles/ molecules on RHS
 increased temperature pushes equilibrium to LHS;
 because (forward) reaction is exothermic
compromise
 if temperature is too high, low yield
 if temperature is too low, slow rate
 if pressure is too high, increased costs/ safety issues
Explain how CCl2F2 in the stratosphere alter the balance of oxygen and ozone. You should include equations in your answer.
 CCl2F2⎯→ CClF2 + Cl
 Accept dotted versions of free radicals.
 Cl + O3 ⎯→ClO + O2
 Cl is regenerated by reaction of ClO with O atoms,
 ClO + O ⎯→ Cl + O2
 O3 ⎯→ O2 + O
 The chain reaction !!!!!!!!!!!!!!!
State two environmental consequences of the presence of nitrogen monoxide
 Acid rain
 Smog
How are these gases formed?
 CO2: combustion
 Methane: anaerobic respiration of organic waste
Why is it necessary to burn substances strongly to achieve decomposition?
 To overcome activation energy
 To break bonds
 Reaction is endothermic (sometimes)
Thomas Midgley inhaled lung full of CCl2F2 and used to blow out a candle. What two features does this show?
 Non toxic
 Non flammable
Explain with reasons two uses of CCl2F2
 Blowing polystyrene: non reactive
 Dry cleaning/degreasing agent: good solvent for organic material
 Fire extinguishers: non flammable
11. Has anyone got a definition sheet

Posted from TSR Mobile
12. (Original post by walkers38)
Am I overcomplicating my head by doing legacy papers? They are so hard!
you are a legend loooooool I did that too the way they come with the weird molecules is absurd !
13. (Original post by Zdavey)
Has anyone got a definition sheet

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Attached Images
14. Chemistry Definitions F322.pdf (207.7 KB, 1153 views)
15. (Original post by walkers38)
Some useful questions from legacy papers

Why do bond enthalpies have negative values?
 Because bond breaking is endothermic
What are the standard conditions?
 298K; 100KPa
State manufacturing process in which hydrogen is used
 Haber process (100atm, 300 degrees)
 Production of margarine
What is meant by exothermic?
 A reaction that releases energy
 Has a negative ΔH
Define the term bond enthalpy
 Energy needed to break one mole of bonds
 In the substance in a gaseous state
Suggest why standard enthalpy change is different from the one calculated from average bond enthalpies?
 Actual bond enthalpies may be different from average values
 Conditions aren’t standard
Suggest why experimental enthalpy change of combustion is different than actual enthalpy change?
 May have been incomplete combustion
 Some heat is lost to the surroundings
Write an equation including state symbols, for the bond enthalpy of I־I
 I – I (g) → 2I (g)
Compare the sustainability of fermentation and hydration in terms of a) availability of starting materials b) energy requirements c) atom economy
Availability
 Sugar renewable because obtained from plants
 Ethane finite because obtained from crude oil
Energy requirements
 Fermentation: energy needed for distillation
 Hydration: energy needed to produce steam
Atom economy
 AE of hydration is 100% which is higher than fermentation’s 51%
 In fermentation, co2 is produced
 In hydration, ethanol is only product
 Improve AE of fermentation by finding a use for CO2
Cis-trans isomerism
 C=C bond restricts rotation
 Each C on C=C is attached to different groups
 Restricted rotation traps the group on one side of double bond
 Give examples
Describe with the aid of suitable diagram, the formation of pi-bond in propene. State the shape and bond angle around each carbon atom [6]
 Pi-bond is formed by sideways overlap of p-orbitals
 Diagram

Why do both cis and trans isomer produce same structural isomer?
 Because C=C restricts rotation
 Product is saturated so no restricted rotation
Outline the processes of how components obtained from fractional distillation are refined with aid of suitable equations. State the importance of products formed in each process [8]
 Cracking: C10H22  C8H18 + C2H4
 Isomerisation: 

 Reforming:  +H2
 The processed products are:
 Used in fuel
 As they are better fuels as they have lower boiling point
 Alkenes from cracking are used in polymer synthesis
 H2 used in Haber Process
Cyclohexene is converted into cyclohexane. What are the reagents and conditions?
 Reagent: H2
 Condition: nickel catalyst
State a suitable reagent for dehydrating alcohol
 H2SO4
Outline how alkenes are used in manufacturing margarine
 Unsaturated oils
 Are hydrogenated
 In presence of nickel catalyst
Outline how alkenes are used in making polymers
 Ziegler-natta catalyst
Difficulty in disposing polymers
 Produce toxic fumes when burnt
 If contains Cl, Cl radicals are also evolved when burnt
Ways to treat waste polymers
 Use as chemical feedstock
 Sorting and recycling
 Cracking to produce organic molecules
 Use gas scrubbers to reduce fumes
What are homologous series?
 Same functional group
 Each successive member differing by CH2
Converting propanol to bromopropane
 Reagent: NaBr/H2SO4
 Condition: heat/reflux
Bromopropane elimination reaction with OH ions makes

Condition required: ethanol
 CH4 + Br2 → CH3Br + HBr
Outline how ethanol is produced industrially from sugars and from ethene. Comment on the decisions that a company needs to consider when deciding which of these methods to use.
sugars
 use of yeast/fermentation ¸
 equation: C6H12O6 → 2C2H5OH + 2CO2
 importance of absence of air/anaerobic conditions
 distil to obtain ethanol
ethene
 use of steam¸with phosphoric acid catalyst
 equation: C2H4 + H2O →C2H5OH ¸
issues for consideration
 availability of raw materials/oil countries use ethene/warm with no oil can grow sugar: use sugar¸
 cost of energy/ethene requires energy but sugars does not¸
 consideration of pollution/effect on the environment¸
What is activation energy?
 Minimum energy required for a reaction to occur
Ammonia, NH3 is made industrially by the Haber process. State the raw materials used to supply the nitrogen and hydrogen for the Haber Process.
 nitrogen: air
 hydrogen: methane/water
In the conditions often used in the Haber process, there is only a 15% yield of ammonia. Suggest what happens to any unreacted nitrogen and hydrogen.
 Recycled
How does nitric acid behave as an acid?
 Proton donor
Construct an equation for the acid-base reaction of ammonia with nitric acid.
 NH3 + HNO3 → NH4NO3
Describe, using one example in each case, the different modes of action of homogeneous and heterogeneous catalysis. [10]
 homogeneous: catalyst in same phase as reactants ¸;
 heterogeneous: catalyst in different phase as reactants ¸
 homogeneous: any example, e.g. Cl in ozone breakdown ¸
 mode of action to match example: forms a intermediate/ClO ¸
 propagation stages shown ¸
 overall equation ¸
 heterogeneous: any example, e.g. Fe in Haber process ¸
 mode of action to match example: reactants adsorbed on surface of catalyst ¸
 weakens bonds in reactants ¸
 reaction takes place and products diffuse from surface of catalyst ¸
Outline why the use of catalysts provides economic benefits to this industry [4]
 reaction proceeds quicker ¸
 lower temperature ¸
 energy costs saved ¸
 more products can be made and therefore more sold ¸
 enable reactions to take place that would be impossible otherwise ¸
Explain the greenhouse effect [3]
 uv from the sun ¸
 released form earth’s surface as i.r. ¸
 i.r. absorbed by molecules of greenhouse gases ¸
Why is carbon dioxide considered to make a significant contribution to the greenhouse effect?
 considerable amounts of greenhouse gases are released by burning fossil fuels
Approximately 79% of the atmosphere consist of nitrogen. Explain why this does not contribute to the greenhouse effect.
 no i.r. active vibrations ¸because no charge on dipole
Describe the structure of a catalytic converter.
 transition metals ¸
 Pt/ Pd/ Rh ¸
 honeycomb structure for maximum surface area
Explain how the design of a catalytic converter allows both carbon monoxide and nitrogen monoxide to be removed.
 oxidation of CO (and unburned hydrocarbons) to CO2 ¸
 reduction of NO to N2 ¸
 2NO(g) + 2CO(g)→N2(g) + 2CO2(g) ¸
 Pd and Pt promote oxidation
 Rh promotes reduction
State le chatelier’s princicle
 when the conditions on a reaction in equilibrium are changed
 the (equilibrium) moves in the direction to minimise the effects of the change
Describe and explain why these conditions are a compromise between rate and equilibrium.
rate
 (increased) pressure increases rate because molecules are closer together/ more concentrated
 (increased) temperature increases rate because molecules are moving faster/ have more energy
equilibrium
 increased pressure pushes equilibrium to RHS; because
 fewer (gas) moles/ molecules on RHS
 increased temperature pushes equilibrium to LHS;
 because (forward) reaction is exothermic
compromise
 if temperature is too high, low yield
 if temperature is too low, slow rate
 if pressure is too high, increased costs/ safety issues
Explain how CCl2F2 in the stratosphere alter the balance of oxygen and ozone. You should include equations in your answer.
 CCl2F2⎯→ CClF2 + Cl
 Accept dotted versions of free radicals.
 Cl + O3 ⎯→ClO + O2
 Cl is regenerated by reaction of ClO with O atoms,
 ClO + O ⎯→ Cl + O2
 O3 ⎯→ O2 + O
 The chain reaction !!!!!!!!!!!!!!!
State two environmental consequences of the presence of nitrogen monoxide
 Acid rain
 Smog
How are these gases formed?
 CO2: combustion
 Methane: anaerobic respiration of organic waste
Why is it necessary to burn substances strongly to achieve decomposition?
 To overcome activation energy
 To break bonds
 Reaction is endothermic (sometimes)
Thomas Midgley inhaled lung full of CCl2F2 and used to blow out a candle. What two features does this show?
 Non toxic
 Non flammable
Explain with reasons two uses of CCl2F2
 Blowing polystyrene: non reactive
 Dry cleaning/degreasing agent: good solvent for organic material
 Fire extinguishers: non flammable
Bond enthalpies have a positive value since bond breaking is endothermic not negative ! oh If am wrong then shame on me
16. In terms of catalysts, do we just need to know that Alkene -> Alkane is Nickel and pretty much everything else is an acid? Or do we have to name the acid?
17. (Original post by hosamthemaster)
Bond enthalpies have a positive value since bond breaking is endothermic not negative ! oh If am wrong then shame on me
Yeah you're right! Please do bear, I typed it all when I was half asleep last night
18. (Original post by FLLF)
In terms of catalysts, do we just need to know that Alkene -> Alkane is Nickel and pretty much everything else is an acid? Or do we have to name the acid?
What I noticed, whenever you add H2 to anything, the catalyst is Nickel. For hydration of ethene, the catalyst is H3PO4 specifically. For everything else its any acid, preferably H2SO4.
19. (Original post by hosamthemaster)
Bond enthalpies have a positive value since bond breaking is endothermic not negative ! oh If am wrong then shame on me
yeah, endothermic gives you +enthalpy value whereas exothermic gives you -enthalpy values.
20. (Original post by Zdavey)
Has anyone got a definition sheet

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Look on GetRevising, that's where I got mine from. I seem to have misplaced the file though...
21. can somebody help me do question 4 on jan 2013

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