energetics Flashcards

1
Q

define enthalpy change

A

overall energy exchanged with the surroundings when a change happens at constant pressure (100kpa) and the final temperature is the same as the starting temperature.

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2
Q

define specific heat capacity

A

the enthalpy in joules which heats 1Kg of substance by 1K

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3
Q

what are standard conditions

A

1mol
100Kpa
298K

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4
Q

define standard enthalpy of combustion

A

enthalpy change when 1mol of substance completely burns in excess 02 under standard conditions 298K 100Kpa

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5
Q

define standard enthalpy change of formation

A

enthalpy change when 1mol of substance is formed from its elements in their standard states under standard conditions 298K 100Kpa

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6
Q

define standard enthalpy change of neutralisation

A

the enthalpy change to form 1mol of water by the reaction of an acid and an alkali under standard conditions 298K 100Kpa

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7
Q

define standard enthalpy change for a reaction

A

the enthalpy change when molar quantities as stated in the equation react under standard conditions 298K 100Kpa

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8
Q

enthalpy (deltaH) =

A

energy transferred (q) KJ / mol

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9
Q

energy transferred (q) =

A

mass of substance heated x specific heat capacity x temperature change

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10
Q

overall enthalpy change =

A

energy to break bonds (+ve) + energy to make bonds (-ve)

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11
Q

endothermic reaction

A

more energy needed to break bonds than make new ones
enthalpy is positive
heat taken in from surroundings

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12
Q

exothermic reaction

A

more energy needed to make new bonds than break existing ones
enthalpy is negative
heat is given out

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13
Q

what is Hess’s law

A

energy in a reaction system must be conserved as energy cannot be created or destroyed.
therefore overall enthalpy change for a reaction is the same regardless of the route taken.

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14
Q

define bond enthalpy

A

energy required to break one mole of bonds in a gaseous state, under standard conditions
298K 100Kpa

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15
Q

what is Gibbs free energy

A

indicator of reaction feasibility
if deltaG is 0 or negative then reaction is feasible

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16
Q

how to calculate Gibbs free energy

A

enthalpy - (Temperature x entropy)

(deltaH - T deltaS)

17
Q

how to calculate minimum temperature a reaction is spontaneously feasible at

A

make deltaG equal to zero

0 = enthalpy - (temperature x entropy of surroundings)

18
Q

why would a reaction not happen even if it was thermodynamically feasible

A

kinetic factors
for example activation energy