enthalpy and entropy Flashcards
1
Q
why are solid ionic compounds stable and have a high melting point
A
- strength of ionic bonds ,electrostatic attractions between opposityley charged ions in the ionic lattice structure
- this creates a substantial energy barrier must be overcome to break down the lattice
2
Q
what is lattice enthalpy
A
measure of the strength of ionic bonding in a giant ionic lattice
3
Q
what is the definition of lattice enthalpy
A
- enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions
4
Q
is lattice enthalpy exothermic or endothermic and why
A
- involves the ionic bond formation from seperate gaseous ions
- it is exothermic change and value for enthalpy change will always be negative
5
Q
describe the two different routes of the born haber cycle
A
- route 1 - formation of gaseous ions, formation of gaseous atom , lattice enthalpy
- route 2 - lattice formation from elements
6
Q
describe the processes in route 1 in the born haber cycle
A
- formation of gasoues atoms - changing the elements in their standard states into gaseous atoms, this change is endothermic as it involves bond breaking
- formation of gaseous ions - changing the gaseous atoms into positive and negative gaseous ions , overall change is endothermic
- lattice formation - changing the gasoues ions into the solid ionic lattice
this is the lattice enthalpy and is exothermic
7
Q
describe the processes in route 2 of the born haber cycle
A
- converts the elements in thir standard state directly to the ionic lattice, one enthalpy change
- enthalpy change of formation
- this is exothermic
8
Q
what is the standard enthalpy change of formation
A
is the enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions with all reactants and products in their standard states
9
Q
what is the compound formed when standard enthalpy change of formation occurs
A
ionic compound in its solid lattice
10
Q
what is the standard enthalpy change of atomisation
A
is the enthalpy change that takes place for the formation of one mole of gaseous atoms from the element in its standard state under standard conditions
11
Q
is the standard enthalpy change of stomisation endothermic or exothermic and why
A
- endothermic
- bond are broken to form gaseous atoms
12
Q
what is the first ionisation energy
A
- enthalpy change required to remove one electron from each atom in one mole of gasouess atoms to form one mole of gasoues 1+ ions
13
Q
are ionisation energies endothermic or exothermic explain why
A
- endothermic because energy is required to overcome the attraction between a negative electron and the positive nucleus
14
Q
what is electron affinity the opposite of ionisation energy
A
- measures the energy to gain electrons
- ionisation energy measures the energy to lose electrrons
15
Q
what is the first electron affinity
A
the enthalpy change that takes place when one electron is added to each atom in one mole of gaseous toms to form one mole of gaseous 1- ions
16
Q
are first electron affinities endothermic or exothermic and why
A
- exothermic as electron being added is attracted in towards the nucleus
17
Q
are second electron affinities are exothermic and endothermic and explain why
A
- endothermic
- second electron being gained by a negative ion which repels the electron away
- so energy must be put in to force the negativley charged electron onto the negative ion
18
Q
describe the process of dissolving ionic compounds
A
- water molecules able to break up the giant ionic lattice struture
- overcome the strong electrostatic attractions between oppositley charged ions
19
Q
what is the standard enthalpy of solution
A
- enthalpy change that takes place when one mole of solute dissolves in a solvent
20
Q
what happens if the solvent is water in the standard enthalpy change of solution
A
- ions from the ionic lattice finish up surrounded with water molecules as aqueous ions
21
Q
is the enthalpy chane of solution be endothermic or exothermic
A
- can be both
- the attraction exists in three dimensions so there will alo be ions and water molecules above and below the plane of the paper
22
Q
describe how water molecules attract the ions in the ionic lattice
A
- negative diple on the oxygen atom is attracted to the positive ion
- the hydrogen atoms is attracted to the negative ion
23
Q
describe the dissolving process
A
- when a solid ionic compound dissolved in water two processes take place:
- the ionic lattice breaks up
- water molecules are attracted to and surround the ions
24
Q
what are the two types of energy changes involved in dissolving
A
- ionic lattice is broken up forming sepetrate gaseous ions
- opposite energy from lattice energy which forms the ionic lattice from gaseous ions
- the seperate gaseous ions interact with polar water molecules to form hydrated aqueous ions the energy change involved is the enthalpy change of hydration
25
what is the enthalpy change of hydration
* the enthalpy change that accompanies the dissolving of gasoues ions in water to form one mole of aqueous ions
26
is the enthalpy change of solution exothermic or endothermic
* an be both depending on the relative sizes of lattice enthalpy and the enthalpy of hydration
27
what are the general properties of ionic compounds
* high metling and boiling points
* soluble in polar solvents
* conduct electricity when molten or in aqueous solutions
28
what is a role of ionic compounds
* coat the inside of furnaces
29
describe the effect of ionic size on melting point
* ionic radius increases
* attraction between ions decreases
* lattice energy is negative
* melting point decreases
30
describe the effect of ionic charge on melting point
* ionic charge increases
* attraction between ions increase
* lattice energy becomes more negative
* melting point increases
31
why are metal oxides used to coat the inside of furnaces
* very exothermic lattice enthalpies and very high melting points
32
describe how ionic radius affects hydration energies
* ionic radius increases
* attraction betwen ion and water molecules decrease
* hydration energy less negative
33
desribe the effect of ionic charge on hydration enthalpy
* ionic charge increases
* attraction with water molecules increases
* hydration energy becomes more negative
34
describe how you can predict solutbility
* requires a quantity of energy equal to the lattic enthalpy
* if the sum of hydration enthalpues is larger than the magnitude of lattice enthalpy the overall enthalpy change (enthalpy change of solution) will be exothermic and compound should dissolve
35
how cn entropy be used to explain things that occur naturally
* gas spreading through a room
* heat from a fire spreading through a room
* ice meltingn in a hot room
36
describe entropy
* energy is dispersd and become more spread out
* natural tendency for energy to spreat our rather than concentrated in one place
* greater the entropy the greater the dispersal of energy the greater the disorder
37
what is the term entropy mean
* dispersal of energy within chemicals making up the chemical system
38
what are the units of entropy
* KK-1Mol-1
39
describe the correlation of entropies with states
* solids have the smallest entropies
* liquids have greater entorpies
* gases have the greatest entropies
40
how do you predict entropy changes
* at 0K there would be no energy and all substances would have an entropy value of 0
* above 0K energy becomes dispersed amongst the particles and all substances have a positive entropy
* systems that are more chaotic have a higher entropy value
41
describe how you can determine if an entropy change is positive or negative
* if a system changes to become more random energy can be spread out more - there will be a positive entropy change
* if a system changes to become less random energy becomes more concentrated - entropy change will be negative
42
what happens when susbtances change state from a solid to a liquid to a gas
* it entropy increases
* melting and boiling increae the randomness of particles
* nergy is spread out more and entropy is positive
43
does entropy increase or decrease from a solid to a liquid
* increases
44
does entropy increase or decrease from a liquid to a gas
increase
45
why does entropy increases from solid->liquid->gas
* changes is state give a more random arrangement of particles
46
describe what happens to entropy when calcium carbonate reacting with hydrochloric acid
* increase in entropy
* production of a gas increase and the disorder of particles
* energy is spread out more and entropy is positive
47
describe what happens to the entropy when nitrogen and hydrogen gas react
* 4 moles of gas -> 2 moles of gas
* there is a decreases in the randomness of particles
* energy is spread out less and entropy is negative
48
what is the standard entropies and why is it standard
* entropy of one mole of a substance under standard conditions
* units JK-1Mol-1
* are always positive
49
how do you calculate entropy changes
* entropy of products - entropy of reactants
50
what does the term feasibility mean
* used to describe wether a reactions isabel to happen and is energetically feasible
* spontaneous - energetically feasible
51
what is free energy
* overall change in energy during a chemical reaction called free energy change
* enthalpy change - heat transfer between the chemical system and the surroundings
* entropy change at the temperature of the reaction - dispersal of energy within the chemical system itself
52
what is gibbs equation
enthalpy change - (temeprature x entropy change)
53
describe the link of a reaction being feasible and free energy
* free energy < 0
* the value for enthalpy larger than entropy
54
describe how endothermic reactions take place at room temeprature
* some ionic compounds idssolve in water at room temperaure in endothermic processes cooling down the water
55
describe the limitations of predications made for feasibility and how it is overcome
* very large activation energy resulting in a very slow rate
* catalyst is used allows the reaction to take place via an alternative route with a lower activation energy
* reduced energy barrier then allows the reaction to take place
