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28 Cards in this Set
- Front
- Back
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Standard conditions |
298K 1atm |
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Standard enthalpy of reaction |
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Standard enthalpy of formation |
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Standard enthalpy of combustion |
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Some chemical reactions are accompanied by enthalpy changes that can be exothermic or endothermic |
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Importance of oxidation as an exothermic process in combustion of fuels, oxidation of carbohydrates such as glucose in respiration |
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Endothermic processes |
Require input of heat energy E.g thermal decomposition of calcium carbonate |
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Enthalpy profile diagrams |
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Activation Energy (Ea) |
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Exothermic and endothermic reactions associated with breaking and making chemical bonds |
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Average bond enthalpy |
Energy required to break 1 mole of a bond in the gas phase, averaged over the different compounds that the bond is found in. |
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Calculate enthalpy change of reaction from average bond enthalpies |
Enthalpy change of reaction = total energy absorbed - total energy released |
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Calculate enthalpy changes |
Q = mcdeltaT |
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Hess' Law |
Enthalpy change for any given process is independent of any intermediate steps providing that starting and finishing conditions for all routes are the same |
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Boltzmann distribution and its relationship with Ea |
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Effect of temperature changes on the proportion of molecules |
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Collision Theory |
In order for a reaction to occur: • |
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Effect of concentration changes on rate of reaction |
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Why might an increase in pressure of gas and concentration may increase the rate of reaction involving gases?? |
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Catalyst |
Speeds up a reaction without being consumed by the overall condition |
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How does a catalyst allow a reaction to occur? |
Provides an alternative reaction pathway Lower Ea |
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Interpret catalytic behaviour in terms of Boltzmann distribution. |
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Catalysts are often enzymes generating specific products and operating close to room temperatures and pressures |
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Catalysts have great economic importance |
Iron in ammonia production Ziegler-Natta catalyst in polyethene Platinum/rhodium in catalytic converters |
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Catalysts... |
Affect the conditions needed for a reaction Lower temperatures Reduce energy demand Reduce CO2 emissions from burning fossil fuels |
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Catalysts enable different reactions to be used with better atom economy and with reduced waste |
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Dynamic equilibrium exists when the rate of the forward reaction is equal to the rate of the reverse reaction. |
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Le Chatelir's principle |
For a closed system in dynamic equilibrium, if any changes are made to the applied conditions the position of equilibrium will shift in such a way as to oppose these changes as far as possible. |
