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Chemistry H > Thermal Chemistry > Flashcards

Thermal Chemistry Flashcards

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1
Q

exothermic

A

releasing heat
- surroundings heat up
- negative heat charge

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2
Q

endothermic

A

absorbs heat
- surroundings cool down
- positive heat charge

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3
Q

flat areas

A

melting/boiling

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4
Q

rising areas

A

heating up H2O

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5
Q

heat

A

always added, related to temperature and phase change

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6
Q

q=mcp∆T

A

heating liquid

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7
Q

q in q=mcp∆T

A

thermal energy (joules)

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8
Q

m in q=mcp∆T

A

mass (grams)

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9
Q

cp in q=mcp∆T

A

specific heat

  • a constant hat varies from substance to substance
  • joules per grams-kelvin (J/g˚C)
  • the amount of energy required to raise 1g of a substance by 1 degrees celsius
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10
Q

∆T in q=mcp∆T

A

change in temperature (kelvin or celsius)

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11
Q

specific heat for identifying unknowns

A
  • putting an unknown object in water allows heat to flow between the unknown and the water
  • thermal equilibrium is reached when temperature becomes the same

(Tf) same for both water & object

  • amount of heat gained/lost by the water is equal to the amount of heat lost/gained by unknown
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12
Q

calorimetry

A

measurement of heat changes for physical and chemical processes

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13
Q

calorimeter

A

measure the amount of heat absorbed or released

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14
Q

Q=n*∆H fus

A

n = number of particles in moles

∆H fus = heat of fusion -> solid to liquid, positive, heat in

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15
Q

Q=n*∆H vap

A

n = number of particles in moles

∆H vap= heat of vaporation -> liquid to gas, positive, heat in

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16
Q

∆H values are given in either

A

Joules per mol (J/mol) or kilojoules per mole (kilo/Joules)

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17
Q

when a substance changes phase

A

there Is a heat value of the change in state for each substance

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18
Q

when you go up the heating curve (solid -> liquid -> gas)

A

endothermic, heat is positive

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19
Q

when you go down the heating curve (gas -> liquid -> solid)

A

exothermic, heat is negative

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20
Q

fus and solid

A

∆H fus = - ∆H solid

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21
Q

vap and cond

A

∆H vap = - ∆H cond

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22
Q

∆H fus

A

s->l
melting

23
Q

-∆H solid

A

l->s
freezing

24
Q

∆H vap

A

l->g
boiling

25
Q

-∆H cond

A

g->l
condensation

26
Q

flat part equation

A

q=mol*∆Hfus

or

q=mol*∆Hvap

27
Q

CpH2O(l)

A

4.18 J/g˚C

28
Q

energy

A

ability to do work (measured in Joules)

29
Q

potential energy

A

stored energy

30
Q

kinetic energy

A

energy of motion

31
Q

heat vs temp

A

temperature is the measure of the average kinetic
- energy of random motions of particles in a substance (measured in degrees)
- heat is the measure of the total amount of energy (measured in joules or calories)

32
Q

temperature change

A

T∆ = Tf - Ti

33
Q

∆T sign

A
  • positive if temp is increasing
  • negative if temp is decreasing
34
Q

heating curve states

A

solid only -> melting (solid/liquid) -> liquid only -> boiling (liquid/gas) -> gas only

35
Q

temperature change

A

solid only, liquid only, gas only

36
Q

phase change

A

melting/boiling

37
Q

heat of fusion

A

is the energy needed to melt one mole

∆Hfus occurs at melting/freezing point
- temperature stays constant!!!!

Q=(∆Hfus)(#moles)

38
Q

constant temperature (heat of fusion)

A
  • solid -> liquid ∆Hfus is positive (heat in
  • liquid -> solid ∆Hfus is negative (heat out)
39
Q

heat of vaporization

A

is the energy needed to boil one mole

occurs at the boiling/condensing point

Q=(∆Hvap)(#moles)

40
Q

constant temperature (heat of vaporization)

A
  • liquid -> gas ∆vap is positive (heat in)
  • gas -> liquid ∆vap is negative (heat out)
41
Q

heat of reaction

A

(∆Hrxn) (or enthalpy): heat energy absorbed or released during a reaction

42
Q

heat of formation

A

(∆Hf) heat energy absorbed or released, in the formation of 1 mole of a compound from its elements

43
Q

heat of solution

A

(∆Hsol): heat energy absorbed or released when a substance dissolves

44
Q

activation energy

A

Ea, energy needed to start a reaction

45
Q

activated complex

A

the unstable arrangement of atoms that exists momentarily at the peak of the activation energy

46
Q

energy diagram

A
  • starts with reactants
  • goes up & down in curve
  • ends with products either higher or lower than before
  • diff in reactants and products is ∆H
47
Q

exothermic energy diagram

A
  • reactants higher than products
  • reactants are less stable than products (higher energy case)
  • products are more stable than products (lower energy case)

∆H rxn = product - reactants = negative

48
Q

endothermic energy diagram

A
  • products higher than reactants
  • reactants are more stable (lower energy state)
  • products are less stable (higher energy state)

∆H rxn = product - reactants = positive

49
Q

cataylsts

A

speed up reactions by lowering the activation energy

50
Q

enthalpy

A

total energy content of a system

51
Q

enthalpy change

A

∆H
the heat energy absorbed or released in an rxn

52
Q

hess’s law

A

the total enthalpy change in a reaction

∆Hrxn = sum of Hfproducts - sum of ∆freactants

53
Q

enthalpy changes

A

1) determine ∆Hrxn for the decomposition of H2O
2) make sure equation is balanced (account 4 moles of each reactant & products)
3) look up ∆Hf for reactants and products on chart (elements are 0!)
4) solve for ∆Hrxn

Chemistry H (11 decks)

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