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physical chem > energetics > Flashcards

energetics Flashcards

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1
Q

reaction system

A

products and reactants part of reaction

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2
Q

surroundings

A

other things like water beaker
air bunsen burner
anything surrounding reaction

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3
Q

factors that effect pressure exerted by surroundings

A

molecules in air
solution in container
lid on beaker or not

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4
Q

constant pressure

A

pressure of reaction system and surroundings and pressure on system dont change

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5
Q

what causes a reaction to give off heat

A

as reactants turn into products energy flows between 2.

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6
Q

heat energy

A

into is taking in energy
out of is give heat

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7
Q

exothermic

A

gives out energy from reaction

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8
Q

endothermic

A

taking in energy from reaction

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9
Q

size of arrow in energy level diagrams

A

shows how much heat energy flows between system and surroundings

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10
Q

what do energy level diagrams show

A

if reaction is endothermic or exothermic and size of heat energy flow

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11
Q

what to include in energy level diagrams

A

x axis energy
y axis progress of reaction
reactants and products curve

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12
Q

reactions under constant pressure

A

heat energy into or out of system and changes temp of surroundings

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13
Q

reactions not under constant pressure

A

changes surrounding temps and how quickly products form and how much product forms

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14
Q

enthalpy change

A

change in amount of heat energy either given it or taken out from the surroundings during a reaction at constant pressure

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15
Q

value of enthalpy change for exothermic

A

negative

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16
Q

value of enthalpy change for endothermic

A

positive

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17
Q

symbol of enthalpy

A

H

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18
Q

change in symbol

A

delta

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19
Q

units of enthalpy change

A

J joules

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20
Q

what are standard conditions

A

atmospheric pressure 100000pa
298K

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21
Q

standard enthalpy changes

A

delta H with circle on top right with line through circle

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22
Q

formation reaction

A

when one mole of a substance is produced from its constituent elements under standard conditions with both reactants and products in their standard states

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23
Q

enthalpy change of formation sign

A

delta small f and H

24
Q

combustion

A

substance plus oxygen is C02 plus water

25
Q

standard enthalpy of combustion

A

enthalpy change when 1 mole of a substance is completely burned in oxygen in standard conditions with all products and reactants in their standard states

26
Q

calorimetry

A

isolate objects surroundings and measure temp change

27
Q

how does mass effect temp

A

more mass is less decrease or increase of temp

28
Q

specific heat capacity

A

amount of energy it takes to increase 1g of a substance by one kelvin

29
Q

SI unit for specific capacity

A

J K-1 g-1

30
Q

q=

A

m c delta T

31
Q

calorimetry when measuring combustion reactions

A

flame calorimetry

32
Q

how to decrease heat energy loss to air

A

increase volume of water
bomb calorimeter

33
Q

calorimetry of reactions in solution

A

constant pressure calorimetry

34
Q

first type of constant pressure

A

zinc mixed with acid

35
Q

thermochemical cycle

A

shows the different possible routes that a reaction can tale from starting reactants to final products

36
Q

enthalpy change of alternative route

A

enthalpy 1 plus enthalpy two

37
Q

hess law direct quote

A

the enthalpy change in a reaction at constant pressure is independent of the route taken

38
Q

another name for alternative route reactions

A

data book reactions

39
Q

data book reactions design

A

alternative route and find total enthalpy change using data book reactions

40
Q

term enthalpy change as applied to a chemical reaction

A

heat energy change at constant pressure

41
Q

improvement to mixing two acids together for enthalpy change

A

use pipette instead of measuring cylinder
insulate beaker/ use cup
reweigh watch glass after adding solid

measure initial and final temp
time intervals

plot temp against time
extrapolate point of adding
find temp change for calculating enthalpy

42
Q

calculating final temp of enthalpy change question

A

when same find moles of chemical
take enthalpy change and times by moles
answer times 1000
100 times 4.18
divide both answers
add answer to initial temp change to get final temp

43
Q

how to improve percentage uncertainty

A

increase concentration

44
Q

equation for temp change

A

q/mc

45
Q

finding temp rise of reaction

A

find moles
times by enthalpy change
temp change is heat energy divided by total mass times specific heat capacity

46
Q

disadvantage of using glass beaker on tripod and gauze

A

glass poorer conductor than copper
tripod and gauze reduce heat transfer

47
Q

why enthalpy of combustions lower than text books

A

incomplete combustion
heat loss to surroundings

48
Q

exam questions on enthalpy of formation to enthalpy change

A

write out direct route
calculate enthalpy of formation of each elements
add formation values to diagram
add up sum of values

49
Q

if reaction balanced in combustion

A

add oxygen balanced for combustion reaction

50
Q

how to get one mole of bonds

A

times the bond enthalpy or long given number by avagadros constant

51
Q

bond dissociation enthalpy

A

energy required to break one mole of a bond in its own atoms in gaseous state

52
Q

how to find bond disscociation enthalpy

A

-take 1 mole of atom
record how many energy it takes for bond to break
-

53
Q

mean bond enthalpies

A

measure the enthalpy change when 1 mole of bonds are broken taken as an mean from a range of different compounds

54
Q

how to calculate atomisation enthalpy

A

-draw out molecules
- calculate how many bonds
-calculate enthalpy from individual energy changes

55
Q

calculating heat capacity exam question

A

moles of substance
moles times amount of energy released
answer divided by temp change

physical chem (8 decks)

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