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Chemistry 12 > u1: enthalpy > Flashcards

u1: enthalpy Flashcards

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1
Q

at molecular level, potential energy is a result of

A
  • forces between nucleus+electrons and between electrons in each atom (bc. like charges repel)
  • forces between protons and neutrons in each nucleus (PEnuclei) (attracted to each other)
  • forces between nuclei and shared electron pair in each bond (PEbond)
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2
Q

at molecular level, kinetic energy is a result of

A
  • molecules moving through space (KEtranslational)
  • molecules rotating (KErotational)
  • bound atoms vibrating (KEvibrational)
  • electron moving within each atom (KEelectron)
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3
Q

definition and variable of enthalpy

A
  • (H)
  • total energy contained in chemical system inc. many kinetic/potential energies
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4
Q

what kinetic/potential energies are involved the total energy contained in a chemical system (enthalpy)

no KE/PE, j say what

A
  • moving electrons in atoms
  • vibration of atoms connected w/ bonds
  • rotational/translational motion of atoms/molecules
  • nuclear potential energy of protons/neutrons in nuclei
  • chemical potential energy of atoms connected by chemical bonds
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5
Q

two types of physical changes

A
  • dissolving
  • phase changes
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6
Q

what changes in bonds occur during dissolving? what is this change known as?

A
  1. bonds between ions or molecules in solute break so that attraction can occur with solvent
  2. bonds between molecules in solvent break so attraction occurs w/ solute
  3. bonds (imfs) form between solute and solvent
    - known as enthalpy of the solution (∆Hsolution)
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7
Q

what changes in bonds occur during phase changes?

A
  • changes to intermolecular bonds occur
  • more ordered to less ordered: energy added from surroundings to system=endotheric
  • less ordered to more ordered: energy released to surroundings from system=exothermic
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8
Q

enthalpy of phase changes and symbols

A
  • solid to liquid: enthalpy of melting (∆H°melt)
  • liquid to gas: enthalpy of vapourization (∆H°vap)
  • gas to liquid: enthalpy of condensation (∆H°cond)
  • liquid to solid: enthalpy of freezing (∆H°fre)
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9
Q

enthalpy of phase change relationships

A

∆H°melt = -∆H°fre
∆H°vap = -∆H°cond

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10
Q

what indicates a chemical change?

A

reactions that produce heat/light, precipitate, gas, or are difficult to reverse

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11
Q

what changes in bonds occur during chemical changes?

A
  1. intramolecular bonds (ionic/covalent/metallic) in reactants break apart
  2. new intramolecular bonds occur to form products
    - both steps require energy
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12
Q

what is required for a chemical reaction to occur

A
  1. bonds within reactants are broken: requires energy = endothermic
  2. bonds are formed between rearranged atoms to form products: releases energy = exothermic
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13
Q

what is the difference between the energy used to break bonds and the energy released to reform new bonds called?

A
  • enthalpy change of the reaction
    -∆Hr
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14
Q

what happens during nuclear decay

A

atoms release neutrons/protons from nuclei to become new elements

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15
Q

what is necessary for nuclear decay to occur

A

a difference between
- binding energy between subatomic particles
- potential energy of nucleus

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16
Q

how is enthalpy measured

A
  • it isn’t possible to directly measure enthalpy of a system so enthalpy differences are measured instead
  • enthalpy difference comes from difference in potential energy that occurs during change of the system
  • this is measured as heat
  • ∆H = Q
17
Q

formula to specifically calculate heat

A
  • ∆H = Q = mC∆T
  • Q = heat (J)
  • m = mass of system (g)
  • C = specific heat capacity (J/g°C)
  • ∆T = Tf - Ti (°C)
18
Q

thermal energy

A

potential energy and kinetic energy

19
Q

why are calorimeters used?

A
  • water absorbs and holds onto thermal energy well
  • also easier
  • prevents thermal energy escaping into surroundings
20
Q

what is a calorimeter

A

double-walled vessel filled with water and equipped with a thermometer and stirring rod

21
Q

how do you find heat/change in enthalpy for calorimeters using ∆H = Q = mC∆T

A
  • use mass and C of water
  • find mass of water using D=m/V
  • D in g/mL
  • m in grams
  • V in mL
22
Q

relationships in calorimetry

A

since ∆Esurroundings = -∆Esystem,
Qsurr = -∆Hsys

23
Q

assumptions of calorimetry and q=mC∆T

A
  • thermal energy exchanges between outside wall in surrounds is minimal and can be ignored
  • any new solution produced in water of calorimeter is dilute, so C of water does not change
  • process in calorimeter occurs under constant pressure

Chemistry 12 (16 decks)

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