energetics

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what is enthalpy change?
heat energy transferred in a reaction at constant pressure. ∆H=kJmol-1
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what are standard conditions?
100kPa and 298K
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what are endothermic reactions?
take in energy from their surroundings. Products have more energy than reactants. ∆H=+ive
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what are exothermic reactions?
give out energy to their surroundings. Products get less energy than reactants. ∆H=-ive
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what is bond breaking?
endothermic
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what is bond making?
exothermic
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why are mean bond enthalpies used?
energy to break a bond varies depending on its location
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why are mean bond enthlpies always positive?
breakinhg bonds is always endothemic
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how do you calculate enthalpy change?
total energy absorbed-total energy released
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what's the enthalpy of reaction?
enthalpy change when a reaction occurs in the molecular quantities shown in the chemical equation, under standard conditions with all reactants and products in their standard states
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what's the enthalpy of formation?
enthalpy change when 1 mole of a compound is formed from its consistuent elements in their standard states under standard conditions
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what's the enthalpy of combustion?
enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions with all reactants and products in standard states
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what is Q=mc∆t
Q-enthalpy change in Joules, m-mass of solution, c-specific heat capacity of water, ∆t-change in temperature
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what does hess's law state?
Total enthalpy change of a reaction is always the same, no matter which route is taken
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Card 2

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what are standard conditions?

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100kPa and 298K

Card 3

Front

what are endothermic reactions?

Back

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Card 4

Front

what are exothermic reactions?

Back

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Card 5

Front

what is bond breaking?

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