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55 Cards in this Set
- Front
- Back
What is the volume of one mole of any gaseous substance at standard temperature and pressure.
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24dm3
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Define standard enthalpy change of combustion.
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The amount of energy released when one mole of fuel is completely combusted.
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What is an exothermic reaction?
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A reaction that GIVES OUT energy to the environment. Enthalpy change of an exothermic is always negative.
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What is an endothermic reaction?
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A reaction that TAKES IN energy from the surroundings. Enthalpy change of an endothermic reaction is always positive.
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Define standard enthalpy change of formation.
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The enthalpy change when one mole of a substance is formed from its constituent elements in their standard state. This can be positive or negative.
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What is entropy.
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Entropy is the number of ways in which particles can be arranged.
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What causes an increase in entropy.
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Change in state from
solid-->lquid-->gas. Mixtures and solutions have greater entropy than unmixed constituents. An increase in the number of particles. |
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What is Hess's law?
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This states that as long as the strating and finishing points of a reaction are the same, the enthalpy change will be always be the same regardless of how you get from start to finish.
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What are enthalpy cycles?
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Enthalpy cycles use Hess's law and often the enthalpy change of formation to determine the enthalpy change of a reaction.
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What is bond enthalpy?
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The average energy required to break the bonds in one mole of gaseous compounds.
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With regards to bond enthalpy, what is bond breaking?
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Bond breaking is always endothermic.
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With regards to bond enthalpy, what is bond making?
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Bond making is always exothermic.
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What determines the strength of a bond?
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A high bond enthalpy means a high bond strength. The shorter a bond the stronger the bond. Double bonds are stronger than single bonds.
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What is functional group in an alcohol?
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A hydroxyl group R-OH
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Should I be able to name alcohols?
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Yes - go and look it up in your revision guide!
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What products do alcohols give when they completely combust?
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Carbon dioxide and water.
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What functional group do ethers have?
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An alkoxy group -OR.
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What are oxygenates?
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Oxygen bearing chemicals that can be added to fuels to increase efficiency, reducing incomplete combustion.
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Give two example of oxygenates.
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Alcohols and ethers.
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What is the general formula for alkanes?
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C(n)H(2n+2)
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What are the structural properties of alkanes?
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They are saturated (all the carbon bonds have single bonds between them).
They are aliphatic (don't contain a benzene ring). |
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What are the products of complete combustion of alkanes?
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Carbon dioxide and water.
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Do I need to know how to name them?
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Yes, so go and learn how.
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What structure and bond angles do alkanes have?
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They are all tetrahedral and have bond angles of 109 degrees.
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What is the general formula of a cycloalkane?
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C(n)H(2n)
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What are the structural properties of cycloalkanes?
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They are saturated and aliphatic (don't contain a benzene ring).
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What is the general formula for alkenes?
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C(n)H(2n)
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What are the structural properties of alkenes?
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They are unsaturated (have a double bond between some of the carbons) and aliphatic (no benzene ring).
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What are the structural properties of arenes?
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They are unsatuated and aromatic (contain a benzene ring).
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What is a structural isomer?
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A molecule that has the same molecular formula, but a different structural formula.(ie the atoms are arranged in a different order).
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What are the three ways of creating a structural isomer?
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1. Differnt carbon chains (ie adding branches).
2. Different position of the functional group. 3. Different functional groups. |
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What is structural isomerism used for?
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To increase the octane number of fuels and prevent auto ignition.
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What does the octane number represent?
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The tendency of a fuel to auto-ignite.
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What does a high octane number mean?
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A low tendency to auto-ignite.
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What problems does auto-ignition cause?
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Knocking, reducing performance and damaging engines.
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What increases octane number?
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Branched alkanes; shorter chain alkanes; making cycloalkanes-->arenes; use of oxygenates.
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What is a catalyst?
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A catalyst is a substance that acts to alter the rate of reaction but is not permanently altered by the reaction.
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What is a heterogeneous catalyst?
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A catalyst in a different physical state to the reactants.
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What is cracking?
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The breaking down of long chain alkanes into shorter ones and alkenes, in order to increase the octane number.
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What is reforming?
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Alkane-->cycloalkane + hydrogen.
Cycloalkane-->arenes + hydrogen. In terms of octane number: arenes > cycloalkanes > alkanes |
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What are the 5 main pollutants from a car engine?
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1. Unburnt hydrocarbons.
2. CO 3. CO2 4. NO(x) 5. SO(x) |
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Where do the unburnt hydrocarbons come from?
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Incomplete combustion of the fuel, some hyrdocarbons are unburnt.
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What is the effect of unburnt hydrocarbons?
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Contribute to the formation of photochemical smog, causing respiratory problems.
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Where does the CO come from?
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Incomplete combustion of the fuel.
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What are the effects of CO?
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Harmful to humans.
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Where does the CO2 come from?
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The complete combustion of the fuel.
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What are the effects of CO2?
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Causes the greenhouse effect and global warming.
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Where do the NO(x) come from?
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Nitrogen from the air reacts with oxygen in the air at the high temperatures in the engine.
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What are the problems of NO(x)?
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Contributes to the formation of photochemical smog. Causes acid rain.
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Where do the SO(x) come from?
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Sulphur impurities in the petrol react with oxygen in the air.
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What are the problems of SO(x)?
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Causes acid rain.
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What is energy density?
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=enthalpy change of combustion * number of moles in 1kg of the fuel. Measured in kJ/kg
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What properties should a good fuel have?
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High energy density.
High octane number. Produce few pollutants. Suitable boiling point. |
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What about hydrogen as a fuel?
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Good - high energy density, and only produces water.
Bad - Unsuitable boiling point (too low) |
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What about ethanol as a fuel?
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Good - renewable, high octane number, oxygenate->less pollutants.
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