Dk Flashcards

Question

What is structural isomers?

Answer 1

Structural isomers are molecules with the same molecular formula but a different structure e.g. chain isomers, position isomers, functional group isomers.

Answer 2

Stereoisomers are molecules with the same structural formula but a different spatial arrangement of atoms e.g. geometric isomers, optical isomers.

Answer 3

The carbon chain of molecules with the same molecular formulae can vary causing isomerism.

Answer 4

Functional groups can be in different positions on the carbon chain resulting in isomers.

Answer 5

Some compounds with the same molecular formula can contain different functional groups.

Answer 6

E/Z isomerism and optical isomerism.

Answer 7

- Would have to break the C=C double bond to rotate around it. - If both C of the C=C have two different groups attached, the molecule has E-Z isomers. -E= entgegan (highest priority opposite). -Z= zusammen (highest priority together).

Answer 8

Molecules have optical isomers if their mirror images are non-superimposable i.e. not the same.

Answer 9

Molecules containing a C with four different groups attached to it exhibit optical isomerism. A carbon atom that has four different groups attached is called a chiral (asymmetric) carbon atom.

Answer 10

Two compounds that are optical isomers of each other are called enantiomers.

Answer 11

A mixture containing a 50/50 mixture of the two isomers (enantiomers) is described as being racemic mixture.

Answer 12

Optical isomers have the same chemical and physical properties as each other, except for their effect on plane polarised light (and how they react with other chiral compounds).

Answer 13

Light is a form of electromagnetic radiation and so consists of waves that vibrate in many directions perpendicular to the direction of travel. Some substances have the ability to remove from normal light all the light waves except those vibrating in a single plane - producing plane-polarised light.

Answer 14

Optical isomers can rotate the plane of polarised light (and so these compounds are said to be optically active).

Answer 15

One enantiomer rotates it in one direction and the other enantiomer rotates it by the same amount in the opposite direction.

Answer 16

A racemic mixture will have no effect on the plane of the light - it is optically inactive (each enantiomer cancels out the effect of the other).

Answer 17

The enthalpy change when 1 mole of electrons is removed from 1 mole of gaseous atoms to from 1 mole of gaseous ions with a +1 charge. X(g)-->X^+(g)+e^- +âˆ†H

Answer 18

The enthalpy change when 1 mole of electron is gained by 1 mole of gaseous atoms to form 1 mole of gaseous ions with a -1 charge. X(g)+e^--->X^-(g) -âˆ†H

Answer 19

up arrow is endothermic, down arrow is exothermic

Answer 20

Lattice enthalpy represents the enthalpy change when the ions in one mole of a solid ionic compound are broken apart (lattice enthalpy of dissociation) or brought together (lattice enthalpy of formation).

Answer 21

The lattice enthalpy of a compound is an indication of the strength of the ionic bonding â€“ the greater the magnitude of the lattice enthalpy, the stronger the bonding. Generally speaking, compounds with smaller ions and/or ions with higher charges have stronger attractions and so greater lattice enthalpy.

Answer 22

Using a Born-Haber cycle

Answer 23

Entropy, S, is a measure of disorder. More order= solid therefore entropy is lower, gas=less ordered therefore higher entropy

Answer 24

E is transferred to surr, E of surr increases, T of surr increases, Entropy, S, of surr increases

Answer 25

E is absorbed from surr, E of surr decreases, T of surr decreases, Entropy, S, of surr decreases

Answer 26

Positive entropy is more likely to happen, things want to become disordered.

Answer 27

system=reaction surroundings=everything else, not reaction

Answer 28

Less likely to happen because the negative change in entropy

Answer 29

Probably positive change in entropy because solid to no solid. However, this reaction is only thermodynamically(heat) feasible but is kinetically(moving) not feasible(4 carbon bonds so can't move, requires large amounts of energy to overcome)

Answer 30

Gibbs free energy change (âˆ†G) combines the two thermodynamic factors of enthalpy change (âˆ†H) and entropy change (âˆ†S).

Answer 31

âˆ†G=kJ/mol âˆ†Hr=kJ/mol T= K âˆ†Ssys= J/mol/K (need to convert to kJ!)

Answer 32

âˆ†G must be negative for a reaction to be feasible, âˆ†G

Answer 33

A decrease in enthalpy (i.e. âˆ†H being negative, i.e. an exothermic reaction) is more favourable in a reaction.

Answer 34

An increase in entropy (i.e. âˆ†S being positive) is more favourable in a reaction.

Answer 35

ï‚· Changes of state are controlled in the same way. ï‚· Below the melting point of a substance, melting is not feasible as âˆ†G is positive, but at the melting point it âˆ†G = 0 and so melting becomes feasible and the substance melts. ï‚· In a similar way, below the boiling point of a substance, boiling is not feasible as âˆ†G is positive, but at the boiling point it âˆ†G = 0 and so boiling becomes feasible and the substance boils.

Answer 36

The position of equilibrium corresponds to the reaction mixture with the maximum value of entropy (of the universe) and the minimum value of Gibbs free energy (of the system).

Answer 37

• The relationship between Gibbs free energy change, (Delta)G(Triple Lines), temperature and the equilibrium constant, Kc, is described by the equation: (Delta)G(triple lines) = -RTInK • The rearrangement of this equation makes it possible to: • Calculate the equilibrium constant • Deduce the position of equilibrium for the reaction In K=-(Delta)G/RT

Answer 38

equilibrium position=lowest point/bottom of the curve âˆ†G for reaction = difference between highest point on both side/axes

Answer 39

âˆ†G= kJ/mol R= J/K/mol T=K R=8.31 gas constant