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Energetic (Bond enthalpies (Average Bond enthalpy (The average bond…
Energetic
Bond enthalpies
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Average Bond enthalpy
The average bond enthalpy is the amount of energy required to break one mole of bonds in the gaseous state averaged across a range of compounds containing that bond.
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Enthalapy
The total energy of a particular compound is the sum of its chemical potential energy and its kinetic energy. This amount of energy is called the enthalpy (symbol H) or heat content.
The change in enthalpy of a reaction is the enthalpy of the
products minus the enthalpy of the reactants
ΔH = HP − HR
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Diagrams
Enthalpy level (energy profile) diagram is a useful tool for visualizing what happens to the enthalpy of a reaction as it proceeds
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Exothermic reaction
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If the enthalpy of the products is less than that of the reactants, a reaction
will lose energy, primarily as heat to its surroundings.
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All combustion reactions are exothermic as, by definition, they release heat energy as a product of the conversion of reactants to products.
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Endothermic reactions
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If the enthalpy of the products is greater than that of the reactants, a reaction will absorb energy as heat from its surroundings.
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The enthalpy change (ΔH) will be negative (less than zero): HP < HR, so ΔH < 0.
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Heat of combustion
Heat of combustion of a fuel. This is the amount of heat produced by the combustion of one mole of the fuel.
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Specific Heat Capacity
Specific heat capacity The energy required to raise the temperature of 1 g of a substance by 1°C. Symbol: c; unit: J °C–1 g–1 or J K–1 g–1
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Hess's Law
Hess’s law A law which states that the heat evolved or absorbed in a chemical process is the same, whether the process takes place in one or in several steps.
Activation Energy
Activation energy The energy required to break the bonds of the reactants and hence allow a reaction to progress. Symbol: Ea
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