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A-LEVEL CHEMISTRY > THERMODYNAMICS > Flashcards

THERMODYNAMICS Flashcards

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1
Q

What is thermodynamics? (1)

A

the study of how heat and temperature relate to energy and work.

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2
Q

what is the born Haber cycle? (1)

A

a way to analyse and break down the enthalpy changes associated with the formation of an ionic compounds.

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3
Q

what is Hess’s law based on? (1)

A

based on the idea that energy is conserved and cannot be destroyed.

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4
Q

what does Hess’s law state? (1)

A

the enthalpy change of a chemical reaction is independent of the path taken.

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5
Q

what is the equation to work out the enthalpy change of formation? (1)

A

enthalpy change of reaction = (sum of) enthalpy change of formation (products) - (sum of) enthalpy change of formation (reactants)

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6
Q

what is the equation to work out the enthalpy change of combustion? (1)

A

enthalpy change of reaction = (sum of) enthalpy change of combustion (reactants) - (sum of) enthalpy change of combustion (products)

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7
Q

what is the standard enthalpy change of formation? (1)

A

the standard enthalpy change of formation is the enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions, all reactants and products in their standard states.

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8
Q

what is the standard molar enthalpy change of combustion? (1)

A

the standard molar enthalpy change of combustion is the enthalpy change when one mole of substance is completely burnt in oxygen.

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9
Q

what is the standard enthalpy of atomisation? (1)

A

the standard enthalpy of atomisation is the enthalpy change which accompanies the formation of one mole of gaseous atoms from the element in its standard state under standard conditions.

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10
Q

what is the first ionisation energy? (1)

A

the first ionisation energy is the standard enthalpy change when one mole of gaseous atoms is converted into a mole of gaseous ions each with a single positive charge.

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11
Q

what is the first electron affinity? (1)

A

the first electron affinity is the standard enthalpy change when a mole of gaseous atoms is converted to a mole of gaseous ions, each with a single negative charge. (exothermic reaction)

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12
Q

what is the second electron affinity? (1)

A

the second electron affinity is the enthalpy change when a mole of electrons is added to a mole of gaseous ions each with a single negative charge to form ions each with two negative charges. (endothermic reaction)

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13
Q

what is the lattice of formation? (1)

A

the lattice of formation is the standard enthalpy change when one mole of solid ionic compounds is formed from its gaseous ions. is always negative

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14
Q

what is the lattice enthalpy of dissociation? (1)

A

the lattice enthalpy of dissociation is the standard enthalpy change when one mole of solid ionic compounds dissociated into its gaseous ions. is always positive

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15
Q

what is the enthalpy of hydration? (1)

A

the enthalpy of hydration is the standard enthalpy change when 1 mole of gaseous ions are converted to aqueous ions.

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16
Q

what is the enthalpy of solution? (1)

A

the enthalpy of solution is the standard enthalpy change when one mole of solute dissolves completely in sufficient solvent to form a solution in which the molecules or ions are far enough apart not to interact with each other.

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17
Q

what is the mean bond enthalpy? (1)

A

the mean bond enthalpy is the enthalpy change when one mole of gaseous molecules each breaks a covalent bond to form two free radicals averaged over a range of compounds.

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18
Q

what is the first step of using a born Haber cycle? (1)

A

start with elements in their standard states

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19
Q

what is the second step of using a born Haber cycle? (1)

A

add in atomisation of element 1

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20
Q

what is the third step of using a born Haber cycle? (1)

A

add in atomisation of element 2

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21
Q

what is the fourth step of using a born Haber cycle? (1)

A

add in ionisation of metal element

22
Q

what is the fifth step of using a born Haber cycle? (1)

A

add in electron affinity of non-metal element

23
Q

what is the sixth step of using a born Haber cycle? (1)

A

add in enthalpy of formation of element 1

24
Q

what is the seventh step of using a born Haber cycle? (1)

A

the final unknown quantity is the lattice formation enthalpy of the ionic compound.

25
Q

what is the bond dissociation enthalpy? (1)

A

the bond dissociation enthalpy is the energy needed to break one mole of gaseous bonds to give separated atoms. is an endothermic process so is a positive value.

26
Q

what factors effect the lattice enthalpy? (2)

A

-the charge on the ion
-the size of the radius

27
Q

what effect does the charge of an ion have on the lattice enthalpy? (1)

A

the charge on the ions increases, the lattice energy increases, as the size of the ions decrease the lattice energy decreases

28
Q

what effect does the size of the radius have on lattice enthalpy? (1)

A

the smaller the ion, the greater the charge density and therefore the force of attraction is greater between ions.

29
Q

why is the second electron affinity endothermic? (1)

A

because they to overcome electron on electron repulsion - electrostatics tell us that like charges repel, the electron is negatively charged and so is the negative ion.

30
Q

what do ionic solvents dissolve well in? (1)

A

ionic solvents dissolve well in polar solvents.

31
Q

what is needed to dissolve an ionic solvent? (1)

A

in order to dissolve an ionic compound the lattice must be broken up, this requires an input of energy (lattice enthalpy)

32
Q

why do some values of enthalpy formation differ? (1)

A

in some ionic compounds there is a large discrepancy between the two values for lattice formation because the bonding in question has covalent character.

33
Q

what does the distortion present in some compounds do to the enthalpy change of formation value? (1)

A

this distortion means there are more electrons than expected concentrated between the metal and non-metal nuclei represents a degree of electron sharing or covalent accounts for the lattice enthalpy of discrepancy.

34
Q

what factors increase polarisation? (2)

A
  • positive ion (small size, high charge)
  • negative ion (large size, high charge)
35
Q

how do you work out the enthalpy change of solution? (3)

A
  • add the enthalpy change for the lattice dissociation of the compound
  • add the enthalpy change for the solution of the metal atom
  • add the enthalpy change for the solution of the non-metal atom
36
Q

what does the perfect ionic model assume? (2)

A

-all bonds are ionic
-all ions are perfect spheres/point charges

37
Q

what effect does covalent character have on the enthalpy change of solution? (2)

A

-if the calculated value is close to that seen in the born Haber cycle it has very little covalent character
-as the amount of covalent character increases the magnitude of the lattice enthalpy calculated from the born Haber cycle becomes greater compared to the perfect ionic model.

38
Q

what occurs in enthalpy change of hydration? (1)

A

when a substance dissolves electrostatic attractions are formed between the polar water molecules and the ion in question.

39
Q

what factors effect the enthalpy change of hydration? (2)

A

-the strength of the attraction between the ion and water, the smaller the ions, the greater the attraction therefore the greater the hydration enthalpy.

40
Q

what is the general trend in hydration enthalpies? (1)

A

hydration enthalpies decrease going down a group.

41
Q

What are the terms feasible and spontaneous used to describe? (1)

A

chemists use the terms feasible or spontaneous to describe reactions that take place on their accord.

42
Q

what in the entropy of a system? (1)

A

the randomness of a system, expressed mathematically

43
Q

how does temperature effect the entropy of a system? (1)

A

entropies increase with temperature, largely because at higher temperatures particles spread out and randomness increases.

44
Q

how can the entropy change of a reaction be calculated? (1)

A

can be calculated by adding all the entropies of the products and subtracting the sum of the entropies of the reactants.

45
Q

what factors govern the feasibility of a reaction? (2)

A

two factors govern the feasibility of a chemical reaction;
-the entropy and enthalpy change.

46
Q

what must the Gibbs free energy change be for it to be a feasible reaction? (1)

A

the result must be negative for the reaction be feasible and will be positive if it is not feasible.

47
Q

what does Gibbs free energy change depend on? (1)

A

depends on temperature meaning that some reactions may be feasible at one temperature but not at another.

48
Q

what is entropy? (1)

A

matter and energy tend to disperse and become more disordered, the degree of disorder is measured by its entropy.

49
Q

when is a system most stable? (1)

A

a system becomes more stable when its energy is spread out in a more disordered state. (most stable in a gas - high entropy)

50
Q
A

A-LEVEL CHEMISTRY (54 decks)

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