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Exothermic reactions
- enthalpy change is negative
- heat is given out
- making of chemical bonds
- Examples: combustion of fuels (CH4 + 2O2 -> CO2 + 2H2O), respiration (C6H12O6 + 6O2 -> 6CO2 + 6H2O)
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Endothermic reactions
- enthalpy change is positive
- heat is taken in
- breaking chemical bonds
- Examples: photosynthesis (6CO2 + 6H20 -> C6H12O6 + 6O2), thermal decomposition (CaCO3 -> CaO + CO2)
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Activation energy
the energy required to start a reaction by breaking bonds
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Standard conditions
- Pressure: 100 kPa / 1 atm
- Temperature: 298K / 25oC
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Enthalpy change of reaction
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Enthalpy change of formation
the enthalpy change when one mole of a compound is formed from its constituent elements in their standard states under standard conditions
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Enthalpy change of combustion
the enthalpy change when one mole of a substance undergoes complete combustion under standard conditions. All reactants and products are in their standard states
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Enthalpy changes
- energy change = mcT
- enthalpy change = -energy change/moles
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Bond enthalpies
energy required to break one mole of gaseous bonds to form gaseous atoms
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Collision theory
- rate increase: more frequent collisions, more successful collisions (increase surface area, increase pressure, increase concentration, increase temperature, use a light source, add a catalyst)
- concentration on rate: increasing concentration increases collisions
- pressure on rate: increasing pressure, particles get closer together, increases frequency of collisions
- temperature on rate: increases temperature, particles get more energy, particle speeds increase
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Chemical industry: compromise
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