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sch4un > unit 2 vocabulary > Flashcards

unit 2 vocabulary Flashcards

1
Q

what is specific heat capacity

A

quantity of thermal energy required to raise the temperature of 1g of a substance by 1 degree celsius

  • measured in J/g(celsius)
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2
Q

Why do your feet burn on the sand but cool off in water if the sun shines on both

A

because sand has a lower heat capacity compared to water (sand gets hotter faster than water does)

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3
Q

what is molar heat capacity

A

amount of heat energy to raise temperature of one mole of a substance by one degree celsius

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4
Q

what assumptions must be made for calorimeter

A
  • any thermal energy transferred from the calorimeter to the outside environment is negligible
  • any thermal energy absorbed by the calorimeter itself is negligible
  • all dilute, aqueous solutions have the same density and specific heat capacity as water
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5
Q

q +

q -

A

+ : endothermic

  • : exothermic
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6
Q

what is the relationship between surroundings and the system

A
  • since matter can’t be created nor destroyed, the total thermal energy of the system and its surroundings remain constant

qsystem+qsurroundings=0

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7
Q

what is enthalpy

A
  • refers to the total value of energy when its at constant pressure
  • its symbolized by the letter H
  • When a system reacts at a constant pressure it’ll either gain/lose energy, thus the enthalpy of the system has gone through a change
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8
Q

relationship between enthalpy and q

A

Hsystem= absolute value of qsystem
as long as pressure is constant

q= energy transfer due to thermal interactions

enthalpy= total energy of thermodynamic system (INCLUDING INTERNAL AND PRESSURE VOLUME ENERGY)

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9
Q

what does total enthalpy depend on

A

total kinetic energy + total potential energy, these values can never be determined which is why we measure change in enthalpy

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10
Q

If enthalpy is greater than reactants

A

absorption: endothermic

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11
Q

if enthalpy is less than reactants

A

release: exothermic

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12
Q

what does energy on the product sign show / negative sign

A

energy is released (exothermic)

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13
Q

what does energy on the reactant sign show / positive sign

A

energy is absorbed (endothermic)

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14
Q

potential energy diagram during endothermic vs exothermic reactions

A

exothermic: high to low (reactants greater than products)

endothermic: low to high (reactants less than products)

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15
Q

bond energies

A

bond energy- amount of energy absorbed or released when a bond is broken/formed

break bond: energy required

form bond: energy released

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16
Q

what is bond enthalpy

A

the enthalpy associated with breaking one mole of a particular bond in a gaseous substance

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17
Q

what is the quantity of energy required to break a chemical bond

A

dissociation energy

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18
Q

why is bond enthalpy always positive

A

energy is required to break chemical bonds

  • energy is always released when a bond forms between gaseous fragments
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19
Q

greater bond enthalpy

A

stronger bond

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20
Q

bond energy per mole sign

A

always positive (bond energy per mole of bonds)

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21
Q

what is thermochemistry

A

the study of the energy changes that accompany physical or chemical changes in matter

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22
Q

what is energy

A

the ability to do work

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23
Q

what is work

A

the amount of energy transferred by a force over a distance

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24
Q

potential energy

A

the energy of a body or system due to its position or composition

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25
Q

kinetic energy

A

the energy of an object due to its motion

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26
Q

thermal energy

A

the total quantity of kinetic and potential energy in a substance

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27
Q

heat

A

the transfer of thermal energy from a warm object to a cooler object

28
Q

temperature

A

a measure of the average kinetic energy of entities in a substance

29
Q

open system

A
  • a system in which both matter and energy are free to enter and leave the system
30
Q

closed system vs open system vs isolated system

A

closed: a system in which energy can enter and leave the system, but matter cannot

isolated: an ideal system in which neither matter nor energy can move in or out

open: both matter and energy are free to enter and leave the system

31
Q

what kind of system is a calorimeter

A

A calorimeter is an example of a closed system

32
Q

heat vs temperature

A

heat:
- thermal energy in motion
- described energy that is flowing from one substances to another due to a diff in temperature

temperature:
- the measure of the average kinetic energy of the entities in a substance
- increasing temperature means the average kinetic energy of the molecules has been increased

33
Q

chemical reactions and energy

A
  • chemical reactions ALWAYS result in breaking of bonds between atoms and the formation of new bonds
  • BREAKING BONDS CONSUMES ENERGY
  • MAKING BONDS RELEASES ENERGY
  • by comparing the energy consumed by bond breakage to the energy released from bonding making, a determination cam be made whether the net result is a storing of energy or release of energy
34
Q

dissociation of NaOH

A
  • when crystals of NaOH are dropped into water, the polar H2O molecules are attracted to the the ions in the crystal, which pull apart and forms a solution
35
Q

chemical reactions in which energy is released

A

exothermic (bonds are being formed, surroundings feel hotter)

endothermic (h2o evaporating: adding energy to break H+ bonds
ex. sweat:
- true to inter and intra molecule

= IMF breaks (pulling energy out of surroundings causing surroundings to be cooler)

36
Q

when energy is broken and it exceeds the energy of a bond, the net result is a decrease in temperature of a solution…

A
  • where energy is being stored in the hydrated ions of the main molecule X
37
Q

are Chem trails forming or breaking bonds?

A

formed bonds, condensing

38
Q

what will happen to temperature in exothermic reactions

A

it will increase
- temp changes in h2o in calorimeter
- closed system (negligible: some energy will be lost)

39
Q

system

surroundings

A

final-initial, reaction

initial-final, h2o

40
Q

increased energy

A
  • increased bond
    (takes more energy to break it)
  • no IMF because they release energy when formed and broken
41
Q

what does the hump on the graph represent

A

activation energy

42
Q

what does the diff between reactants and products on the graph represent

A

change in enthalpy

43
Q

which reactions are endothermic?
exothermic?

A

endothermic: melting, fusion, vapourization, sublimination
exothermic: dissolving, freezing, condensation, and deposition

44
Q

How do you calculate enthalpy change

A

= (sum of moles of products(enthalpies of products)) - (sum of moles of reactants(enthalpies of reactants))

45
Q

what is the rate of a reaction

A

change in concentration/change in time

46
Q

negative slope

A

rate of consumption of reactants decreases

47
Q

positive slope

A

rate of products produced increased

48
Q

gradient of tangent to any point on the curve

A

rate of reaction at any instant

49
Q

steeper the gradient

A

faster the reaction

50
Q

at start of reaction, graph is the steepest

A

rate at the start of any reaction is always the fastest

51
Q

as reaction progresses, gradient is becoming gentler

A

reaction is slowing down

52
Q

after sometime, the graph levels off

A

point of levelling off signifies the end of the reaction

53
Q

chemical nature of the reactants

A
  • the more reactive the substance is, the faster the rate of the reaction
  • unreactive metals like gold oxidize very slowly
  • other metals like alkali’s oxidize very quickly
54
Q

concentration of reactants

A

the rate of many chemical reactions increases at higher concentration of reactants

55
Q

surface area

A

the greater the surface area, the more collisions of particles takes place and the faster the reaction

56
Q

temperature

A

an increase in temperature increases kinetic energy of the particles, this in turn, increases the number of collisions and therefore the rate of the reaction

57
Q

catalyst

A
  • substance that alters the rate of a chemical reaction without itself being permanently changed
  • provide an alternative energy pathway for the reaction, this lowers activation energy allowing more molecules to overcome the activation energy and produce products at a faster rate
  • a catalytic converter increases the rate at which exhaust gases react with oxygen so that more of the exhaust products will be oxidized into harmless or less harmless substances
58
Q

Collision theory

A
  • chemical reactions can only occur if reactants collide with proper orientation and with enough kinetic energy to break reactant bonds and form product bonds

(an ineffective collision of oxygen and hydrogen molecules produces no reaction; the reactants bounce back unchanged)

(an effective collision of hydrogen and oxygen molecules produces water molecules)

59
Q

sufficient energy + correct orientation in collision theory

A

sufficient energy:
- minimum amount of energy a reactant must have for a collision to be effective is called the activation energy
- overcomes the electrostatic repulsive forces between colliding entities
- weakening the bond of the

correct orientation:
- direct contact is requires for a equation to occur
there may be many collisions but only those that are in the proper reaction will cause a reaction to fell safe.

60
Q

activation energy

A

minimum energy that colliding particles have to react, barrier for reactants to pass

61
Q

describing reaction rates

A

when 2 reactant particles collide, they form as an activated complex which is an unstable form of electrons that forms a peak of the activation energy barrier and is short lived

62
Q

what do catalysts do

A

speed up the reaction by lowering activation energy

63
Q

enthalpy (catalyst graph slide)

A

enthalpy rises as reaction starts, energy is being put in to break bonds

64
Q

Maxwell-boltzmann distribution

A

the area under the curve Ea, corresponds to the number of molecules with sufficient energy to overcome this barrier and rest

  • if a catalyst is added, the activation energy is lowered, Ea will move to the left
  • greater area under the curve, showing molecules have sufficient energy to overcome barrier in excess due to lowering of activation energy

-due to the many collisions taking place in gases , there is a spread of molecular energy and velocity

65
Q

relative rates of reactions in order

A

electron transfer
collisions btwn 2 reactants
collisions btw multiple reactants
bond rearrangements
heterogeneous reactions (interface site)

sch4un (9 decks)

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