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57 Cards in this Set

  • Front
  • Back

One mole of gas at STP occupies:

24 cubic decimetres
The enthalpy change of combustion:
The energy released when one mole of a substance burns COMPLETELY at STP. Always a negative value.
Standard conditions are:
25 degrees centigrade at one atmosphere pressure.
Exothermic reactions:
Give off energy from the system to the surroundings. Surroundings temperature increase. Always a negative value for enthalpy.
Endothermic reactions:
Take in energy from the surroundings into the system. The temperature of the surroundings decrease. Value positive.
Factors in the accuracy of calorimetry:
Heat loss. Hear to the instruments. Differences in specific heat capacity. Evaporation of fuel. Inaccuracy in measuring mass. Incomplete combustion.
Equation for calorimetry energy transfer:
cm(delta)T
Entropy:
The number of ways in which particles (molecules) can be arranged OR a measure of disorder in a system.
Increase entropy:
With higher energy states (solid, liquid, gas) or by mixing or dissolving constituents AND if products have more moles.
Hess's law states that:
As long as a chemical reaction has identical conditions (STP), starting and finishing points, the enthalpy change will be the same regardless of route.
When writing constituent relents for formation reactions:
Write them in molecular format: eg H2.
Bond enthalpy is:
The average amount of energy needed to break the bonds of one mole of a gaseous compound.
Strong bonds:
Have high bond enthalpies, and are generally short or multiple bonds.
Alcohols have the x functional group
Hydroxyl.
Ethers have the x functional group
Alkoxy.
When naming ethers, which chain takes precedence?
Shorter.
Oxygenates include:
Alcohols and ethers.
Hydrocarbons are separated by:
Fractional distillation.
Aliphatic compounds include:
Only open-chain hydrocarbons.
Open-chain alkanes are:
Saturated aliphatic hydrocarbons.
Cycloalkanes are:
Not aromatic. Saturated.
Alkanes are:
Aliphatic, unsaturated.
Arenes:
Contain benzene and are unsaturated, aromatic.
Structural isomers:
Have the same molecular formulae but different structural formulae. Same amount and types of atoms, different arrangement in space and different structures
Chain isomerism:
Differences in the lengths of carbon chains. Typical of side chain alkanes. Same amount and types of atoms, different arrangement in space and different structures
Positional isomerism:
The same functional group in different positions. Same amount and types of atoms, different arrangement in space and different structures
Functional group isomerism:
Same molecular formula but different functional groups. Alcohols and ethers do this. Same amount and types of atoms, different arrangement in space and different structures
Isomerisation:
Increases octane number by forming branched alkanes from straight-chain alkanes. Platinum catalyst and heat.
Auto-ignition is:
The explosion of a fuel without a spark (due to temperature and heat)
Auto-ignition is undesirable because:
It reduces efficiency, causes knocking, and damages the engine cylinder.
Octane number is:
A measure of the tendency of a fuel to auto-ignite. High is lower tendency. High desirable in petrol engines.
Cetane number is:
Similar to octane number. High is a high tendency to auto ignite, desirable in diesel engine.
Increase octane number by:
Isomerisation, cracking, reforming, oxygenating.
Low octane numbers belong to:
Long, unbranched, deoxygenated, aliphatic alkanes.
When writing full structural formulae:
Include ALL bonds.
Catalysts are:
Chemicals which speed up a chemical reaction by providing an alternate path of lower activation enthalpy. Emerges unchanged at the end of the reaction.
Heterogenous catalysts:
Are in a different state to the reactants.
Catalytic converters contain:
Platinum, rhodium.
Catalyst poisons:
Adsorb to a catalyst surface, do not desorb. Prevent adsorption of substrate, saturate catalyst.
An effective catalyst:
Should have a large surface area, and be easily regenerated.
Stages of heterogenous catalysis:
Reactants adsorb onto surface; of catalyst; bonds in reactants weaken and break; new product bonds and products are formed; products desorb and diffuse away.
Cracking:
Produces shorter chains, usually a branched alkane and an alkene. Zeolite catalyst. Increases octane number.
Reforming:
Produces cycloalkanes and hydrogen, then arenes and hydrogen. Platinum catalyst. Increases octane number.
Isomerisation:
Produces more branched products. Increases octane number. Platinum catalyst. Zeolite is a sieve.
Unburnt hydrocarbons:
Formed by evaporation and incomplete combustion. PC smog and respiratory problems. Reduced by CCs and oxygenates.
Carbon monoxide:
Incomplete combustion. Toxic to humans, blocks blood oxygen uptake. Reduced by CCs, oxygenates and lean burn engines.
Carbon dioxide:
Complete combustion produces this. Contributes to global warming/greenhouse gas. Only hydrogen avoids this.
Sulphur oxides:
Sulphur in fuel reacting with oxygen under engine conditions. Causes acid rain. Use low sulphur petrol to reduce.
Nitrogen oxides:
Nitrogen and oxygen from air react at high heats and pressures in engine. PC smog, respiratory problems, acid rain. Reduced by CCs and lean burn.
Diesel:
Unsustainable. Less CO than petrol, readily available. Produce more NOx and particulates than a petrol engine.
Pariculates
Incomplete combustion produces C atoms. Causes sooty buildup, respiratory problems.
LPG and autogas:
Unsustainable (fossil fuel) produces less CO, CO2, CxHy and NOx than petrol. Petrol engines can be easily converted. Needs high pressure storage to be a liquid.
Ethanol:
Only sustainable if energy is that is needed for growing and processing (fermentation). Less CO, SO2 and NOx than normal engines. High octane number. Oxygenate. Sugar cane absorbs CO2 to grow. Highly flammable.
Biodiesel:
Can be made from preexisting waste biomass. Renewable so long as processing energy is. Biomass had absorbed CO2, biodegradable. Less CO, CxHy, SO2 and particulates than a diesel engine. More NOx.
Hydrogen:
Sustainable so long as energy used (electrolysis) is renewable. Water is only combustion product. Needs high pressure secure (non-leaky) storage. Highly flammable.
Reasons why calorimetry might produce a value different to those suggested by average bond enthalpies: (5)
The combustion/reaction may have been incomplete; the fuel may have evaporated (if liquid); the experiment may have been conducted at non-standard conditions; bond enthalpies are average; bond enthalpies apply to the gas phase (if fuel not gas)
Zeolites make good catalysts in which process and why?
Catalytic cracking. Because reactions take place on a catalyst surface (which reactants adsorb onto) and zeolites have a large surface area.