2015 Chains, Energy and Resources Flashcards
What is meant by the term structural isomers
• ( Compounds or molecules having the) same molecular
formula but different structural formulae
Alkanes in crude oil can be used to manufacture ethene. Two stages are required
Name the stages
• Fractional distillation AND cracking
Write an equation for the preparation of ethene from an alkene
• C10H22 → C8H18 + C2H4
Describe and explain the effect of increasing the pressure on the reaction rate
CO2+3H2 → CH3OH+H2O ∆H=-49
- Increased rate
- Greater concentration of molecules
- More collisions per second / more frequent collisions
What is meant by average bond enthalpy
• (Average enthalpy change) when one mole of bonds of (gaseous covalent) bonds is broken
State le Chatelier Priciple
• The (position of a dynamic) equilibrium shifts to minimise (the effect of) any change
Higher pressures and low temperatures would give a maximum equilibrium yield of methanol
Explain this statement in terms of le Chatelier’s principle
CO2+3H2 → CH3OH+H2O ∆H=-49
Pressure
• Right-hand side has fewer (gaseous) moles/molecules
Temperature
• (Forward) reaction is exothermic
OR reverse reaction is endothermic
Equilibrium
• Lower temperature/cooling AND increasing pressure
shifts (equilibrium position) to the right
Explain why the actual conditions used by the chemical industry might be different
• Low temperature gives a slow rate
OR high temperatures needed to increase rate
• High pressure is expensive (to generate)
OR high pressure provides a safety risk
Explain why the use of a catalyst can reduce the demand for energy
• Allows reactions to take place at lower temperatures
Compound G was once used as a propellant in aerosols. Compound G has been linked with depletion of the ozone layer in the stratosphere
State two properties that made compound G suitable for use as an aerosol
- Low reactivity OR will not burn/non-flammable
- Volatile OR low boiling point
- Non-poisonous OR non-toxic
Explain the following statements, using equations where appropriate.
• Life on Earth benefits from the presence of an ozone layer
• The concentration of ozone is maintained in the ozone layer
• Compound G produces radicals which catalyse the breakdown of ozone
Benefit of ozone layer to life • Ozone absorbs UV (radiation) • Maintenance of O3 concentration • O3 → O2 + O Production of radicals from • CF2Cl2 → Cl + CF2Cl Breakdown of O3 Cl+O3→ ClO+O2
What happens to molecules when infrared radiation is absorbed
- Bond vibrates more
- Bond bends more
- Bond stretches more
What is meant by the term homologous series
• Series of compounds with the same functional group but with each successive member by CH2
Allyl bromide, CH2=CH2Br
What is the general formula of the homologous series that has allyl bromide as a member
• CnH2n–1Br
What does a curly arrow represent in mechanisms
• Movement of an electron pair
