Physical Chemistry

Question 1

law of conservation of energy

Answer 1

the overall amount of energy does not change as energy is conserved in reactions, energy can only be transferred, not created or destroyed

Question 2

neutralisation heat change

Answer 2

give energy out, exothermic

Question 3

displacement reaction heat change

Answer 3

can take energy in or give it out

Question 4

combustion heat change

Answer 4

always give energy out, exothermic

Question 5

heat energy change equation

Answer 5

Q = m x c x ΔT

Question 6

what is specific heat capacity

Answer 6

the energy needed to raise the temperature of 1g of a substance by 1C

Question 7

energy level diagram for exothermic

Answer 7

-energy change is negative, energy of products are lower than reactants
-downwards arrow

Question 8

energy level diagram for endothermic

Answer 8

-energy change is positive, energy of products are high than reactants
-upwards arrow

Question 9

what is the change in energy when breaking bonds

Answer 9

-endothermic as energy is taken in to break bonds

Question 10

what is the change in energy when making bodns

Answer 10

-exothermic as energy is released when new bonds are formed

Question 11

exothermic reaction bond energies

Answer 11

MEXO>BENDO
-energy from bonds made is greater than energy lost from making bonds, so heat is released
-negative enthalpy change value as reactants have more energy than products

Question 12

endothermic reaction bond energies

Answer 12

BENDO>MEXO
-energy lost from breaking bonds is greater than the energy released from making bonds, so energy is taken in
-positive enthalpy change value as products have more energy than reactants

Question 13

enthalpy change equation

Answer 13

energy taken in (bonds broken) - energy given out (bonds made)

Question 14

experiment to see effect of surface area of a solid on the rate of reaction

Answer 14

1. add dilute HCl to a conical flask
2. use a delivery tube to connect the flask(with a bung) to an inverted measuring cylinder (with water in it) upside down in a water trough.
3. add calcium carbonate chips into the conical flask and close the bung
4. measure the volume of gas produced in a fixed time using the measuring cylinder
5. repeat with different sizes of calcium carbonate chips

Question 15

experiment to see the effect of concentration of solution on the rate of reaction

Answer 15

-

Question 16

factors affecting the rate of reaction

Answer 16

-concentration of the reactants in solution or the pressure of reacting gases
-temperature
-surface area of solid reactants
-presence of a catalyst

Question 17

explain how concentration affects the rate of reaction

Answer 17

-more reactant particles in a given volume
-more collisions per second
-increases the frequency of successful collisions per second
-rate of reaction increases
(#of collisions is proportional to #of particles)

Question 18

explain how increasing pressure affects the rate of reaction

Answer 18

-increasing pressure means there is the same number of reactant particles in a smaller volume
-more collisions per second
-increases the frequency of successful collisions
-rate of reaction increases

Question 19

explain how temperature affects the rate of reaction

Answer 19

-increasing temperature means particles have more kinetic energy
-causes more collisions per second
-greater frequency of successful collisions per second
-rate of reaction increases

Question 20

how does the surface area affect the rate of reaction

Answer 20

-increasing the surface area means a greater surface area of particles will be exposed to the other reactant
-more collisions per second
-greater frequency of successful collisions per second
-rate of reaction increase
(surface area is directly proportional to the number of collisions per second

Question 21

what are catalysts

Answer 21

substances which speed up the rate of reaction without themselves being altered or consumed in the reaction (same mass before and after)

Question 22

how do catalysts work

Answer 22

-they provide an alternative pathway for the reaction to occur
-alternative pathway has a lower activation energy, so a greater proportion of molecules have sufficient energy for an effective collision

Question 23

why are transition metals used as catalysts

Answer 23

they have variable oxidation states allowing them to readily donate and accept different numbers of electrons

Question 24

how is activation energy represented on energy level diagrams

Answer 24

initial increase in energy from the reactants to the peak of the curve
-the greater the activation energy the greater the heat needed

Question 25

reversible reactions

Answer 25

the reaction can occur in both directions

Question 26

thermal decomposition of ammonium chloride word equation and observations

Answer 26

ammonium chloride ⇌ ammonia + hydrogen chloride (in heat is forward, when the gases cool it is the backward reaction) -white solid formed (ammonium chloride) at the bottom of the test tube -white smoke also formed (NH3 and HCl mixed)

Question 27

dehydration of hydrated copper II sulfate word equation and observations

Answer 27

hydrated copper(II) sulfate ⇌ anhydrous copper(II) sulfate + water (heat up for forward, add water for backwards) -blue crystals initially, which is heated, where white crystals/powder is formed -adding water makes blue crystals again -exothermic reaction

Question 28

what is equilibrium

Answer 28

when the rate of forward reaction equals the rate of the reverse rection, and there is a constant concentration of reactants and products

Question 29

conditions for dynamic equlibrium

Answer 29

-constant concentration of products and reactants (no change to the system such as temp or pressure) -closed system (nothing can leave or enter)

Question 30

rate of forward and reverse reaction during the progress of a reaction graph

Answer 30

look it up

Question 31

what does it mean if the position of equilibrium shifts to the right

Answer 31

-the forward reaction is favoured -increases in the amount of products formed

Question 32

what happens if the temperature of a reversible reaction increases

Answer 32

the equilibrium will shift in the direction of the endothermic reaction

Question 33

what happens if the pressure of a reversible reaction increases

Answer 33

-the reaction that produces the least number of moles of gases

Question 34

effect of catalysts on equilibrium

Answer 34

-no effect as both the forward and backward rate of reaction are increased by the same amount -the reaction will reach equilibrium faster