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EDEXCEL AS Chemistry > energetics > Flashcards

energetics Flashcards

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1
Q

enthalpy change of a reaction definition…

A

the enthalpy change when quantities of substances in standard states react under standard conditions

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2
Q

enthalpy change of formation definition…

A

the enthalpy change when one mole of a substance is produced from its elements under standard conditions

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3
Q

enthalpy change of combustion definition…

A

the enthalpy change when one mole of a substance is burned completely in oxygen under standard conditions

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4
Q

enthalpy change of neutralisation definition…

A

the enthalpy change when solutions of acid and alkali react together under standard conditions to produce one mole of water

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5
Q

bond enthalpy definition…

A

the energy required to break one mole of the stated bond in a gaseous state, under standard conditions

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6
Q

specific heat capacity definition…

A

the energy required to raise the temperature of 1g of a substance by 1K without a change of state

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7
Q

endothermic reaction…

A

a reaction that absorbs energy from its surroundings- the energy change is positive

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8
Q

exothermic reaction…

A

a reaction which releases energy to the surroundings- the energy change is negative

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9
Q

enthalpy change is…

A

heat energy change

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10
Q

enthalpy change symbol…

A

🔺H

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11
Q

enthalpy is measured under…

A

standard conditions (100 kPa pressure and a specified temperature, generally 298K)

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12
Q

when bonds are broken, energy is…

A

taken in from the surroundings (endothermic)

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13
Q

when bonds are formed, energy is…

A

given out to the surroundings (exothermic)

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14
Q

overall enthalpy change can be calculated by…

A

🔺H = energy to break bonds (+ve) + energy to make bonds (-ve)

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15
Q

enthalpy changes in a react can be shown on…

A

an energy level diagram

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16
Q

energy level diagrams indicate…

A

if a reaction is endothermic or exothermic

17
Q

endothermic energy level diagram…

A

reactants below products

18
Q

exothermic energy level diagram…

A

reactants above products

19
Q

in endothermic reactions, more energy is needed to…

A

break bonds than make new ones, therefore overall enthalpy change is positive, and heat is taken in from the surroundings

20
Q

in exothermic reactions, more energy is needed to…

A

make new bonds than break existing ones, therefore overall enthalpy change is negative, and heat is given out to the surroundings

21
Q

energy change equation…

A

q=mc🔺T
(q= energy change (J), m= mass (g), c= specific heat capacity (J g-1 .C-1, 🔺T= temperature change(C))

22
Q

using q=mc🔺T, enthalpy change per mole of a substance can be calculated- equation…

A

🔺H = q/moles

23
Q

sources of error with 🔺H values…

A
  • heat loss due to conduction, convection or inaccuracies in measuring temperatures.
  • the specific heat capacity is taken to be 4.18 which is the value for water, and not the actual solution. the SHC of the calorimeter isn’t taken into account so this leads to inaccuracies in the calculation
24
Q

heat loss to the surroundings can be reduced by…

A
  • putting a lid on the calorimeter
  • insulating the outsides of the calorimeter using an insulator like polystyrene
25
Q

enthalpy of formation arrows

A

flip reactants
follow products

26
Q

enthalpy of combustion arrows

A

follow reactants
flip products

27
Q

bonds with lower bond enthalpy are expected to…

A

break first

28
Q

if a reaction is endothermic overall, then it is likely that the reaction will…

A

occur slowly at room temperature

29
Q

mean bond enthalpy values can be used to calculate the…

A

overall enthalpy change for a reaction

30
Q

overall bond enthalpy change equation…

A

🔺rH= bond breaking-bond forming

31
Q

Hess’s Law

A

the enthalpy change of any reaction is independent of the path taken

EDEXCEL AS Chemistry (13 decks)

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