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55 Cards in this Set

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