module 4

Question 1

what breaking bonds

Answer 1

energy is absorbed

Question 2

forming bonds

Answer 2

energy is released

Question 3

exothermic reactions

Answer 3

• release energy
• temperature increases
• bond forming is greater than bond breaking

Question 4

endothermic reactions

Answer 4

• absorb energy
• temperature decreases
• bond breaking is greater than bond forming

Question 5

solute dissolves in solvent to form a solution

Answer 5

solute -solute bonds: broken (requires energy –> endothermic):
- ionic lattice held together by ionic bonds –> forces
of electrostatic attraction between positively and
negatively charged ions
solvent-solvent bonds: broken (requires energy –> endothermic):
- liquid state (water molecules are held together by
intermolecular forces eg. hydrogen bonding, dipole
- dipole interactions, dispersion forces)
solute-solvent interactions: formed (between ions and water molecules –> energy is released –> exothermic)
- solvation/hydration(case of water) –> solvent
molecules form hydration spheres around
individual ions
- the ion - dipole forces are formed between the
ions and the water molecules are. formed –>
stronger than hydrogen bonding in water
molecules

Question 6

exothermic and endothermic dissolution of salts

Answer 6

• more energy required to break solute - solute and solvent - solvent (salit dissolves exothermically)
• less energy required to break solute - solute and solvent - solvent (salt dissolves endothermically)

Question 7

salt that dissolves endothermically

Answer 7

• less energy required to break solute solute and solvent solvent interactions
  eg. KCl

Question 7

salt that dissolves exothermically

Answer 7

• more energy required to break solvent solvent and solute solute
  eg. NaOH

Question 8

molar heat of a solution (dissolution)

Answer 8

molar enthalpy change (delta H) (quantity of heat released upon the dissolution of one mole of a particular substance)
- J or kJ
- delta H = -q/n
- q = J

Question 9

enthalpy

Answer 9

amount. of stored heat energy within a substance
H reaction = h products - h reactants
- reactants > products (exo) (more energy for bond forming)
- reactants < products (endo) ( more energy for bond breaking)

Question 10

law of conservation of energy

Answer 10

energy cannot be created nor destroyed oonly reaaranged

Question 11

transition state/activated complex

Answer 11

point in the reaction pathway between breaking and forming new covalent bonds

Question 12

bond breaking

Answer 12

• absorbs energy
• delta H > 0
• endo
• positive

Question 13

bond forming

Answer 13

• releases energy
• delta H < 0
• exo
• negative

Question 14

energy profile diagrams

Answer 14

• change in enthalpy as the reaction proceeds
• larger the activation complex th emore enery that is required to start the reaction
  x - axis: reaction pathway
  y - axis: potential energy (kj)

Question 15

heat released (q)

Answer 15

q = mcAt
- q = J
- m = g
- c = J
- T = K

Question 16

calorimetry

Answer 16

study of enthalpy changes in a reaction

Question 17

percentage error

Answer 17

%error = 100% X |theoretical value - experimental value|/|theoretical value|

Question 18

do chemical bonds store energy

Answer 18

no

Question 19

bond energy

Answer 19

amount of energy required to break a bond
- bonded has less energy than those that are unbonded

Question 20

hess’s law

Answer 20

states that the enthalpy change accompanying a chemical change is independent of the route by which the chemical change occurs
- used to measure the enthalpy changes of a reaction

Question 21

hess’s cycles/energy cycle diagram

Answer 21

represents the enthalpy changes in a system of reactions

Question 22

standard enthalpy of formation

Answer 22

change in enthalpy associated with the formation of 1 mol of a substance in its standard state from its constituent elements in their standard state

Question 23

HAVE NO FEAR OF ICE COLD BEER

Answer 23

diatomic atoms

Question 24

enthalpy change

Answer 24

delta H = sum of products - sum of reactants

Question 25

enthalpy in combustion

Answer 25

exothermic --> negative

Question 26

enthalpy in photosynthesis

Answer 26

endothermic --> positive (reversed = cellular respiration)

Question 27

two types of catalysts

Answer 27

homogeneous: same state as reactants - usually all in aqueous/liquid/gaseous state - reacts with one or more of the reactants to form a temporary immediate - immediate reacts with the other reactants and decomposes to form products of reaction - process regenerates the catalyst --> not consumed therefore - eg. decomposition of ozone heterogeneous: different state as reactants - usually solid catalyst in a liquid/gaseous/aqueous reaction - reactants adsorbs to the catalyst at active sites - chemical reaction takes place on the surface of the catalyst - product the desorbs from the surface

Question 28

intermediate

Answer 28

temporary species in a chemical reaction formed from a sub-reaction - not considered a reactant or a product

Question 29

bond breaking

Answer 29

h reaction = h bond breaking + h bond forming - reverse the sign of bond forming

Question 30

haber process

Answer 30

production of ammonia from its constituent gaseous elements

Question 31

entropy

Answer 31

amount of randomness or lack of ordered structure - J delta s = sum of s products - sum of s reactants

Question 32

differences between entropy and enthalpy

Answer 32

- enthalpy = change - entropy = absolute

Question 33

spontaneous

Answer 33

a process that will naturally occur without any ongoing external energy

Question 34

exothermic and endothermic entropy

Answer 34

exothermic: - heat released - increases kinetic energy - particles move faster - increases entropy endothermic: - heat absorbed - decreases kinetic energy - decreases entropy

Question 35

what are the drivers of reactions

Answer 35

enthalpy drive and entropy drive

Question 36

forward enthalpy/entropy drive

Answer 36

- enthalpy: delta H < 0 - entropy: delta S > 0 - spontaneous

Question 37

reverse entropy/enthalpy drive

Answer 37

- enthalpy: delta H > 0 - entropy: delta S < 0 - non-spontaneous

Question 38

gibbs free energy

Answer 38

- refers to the maximum amount of work that can be performed by a thermodynamic system during a chemical process delta G = delta H -T delta S - usually J delta G < 0 = spontaneous - reaction will go to completion without an external energy input (usually a flame at the start) (exergonic) delta G > 0 = non-spontaneous - continuous energy input is required to force the reaction to occur (endergonic) delta G = 0 - neither spontaneous or non-spontaneous

Question 39

H> 0 S<0

Answer 39

are never spontaneous as it will always be positive

Question 40

H< 0 S> 0

Answer 40

always be spontaneous because delta G will always be negative