Topic 3

Question 1

define standard enthalpy change of reaction

Answer 1

the enthalpy change that accompanies a reaction under standard conditions and all reactants and products are in standard state

Question 2

define standard enthalpy change of formation

Answer 2

the enthalpy change when 1 mole of a compound is formed from its constituent elements under standard conditions when all reactants and products are in standard state

Question 3

define standard enthalpy change of combustion

Answer 3

the enthalpy change when 1 mol of a substance completely reacts with oxygen under standard conditions and all reactants and products are in standard state

Question 4

define exothermic

Answer 4

heat energy is lost to the surroundings. the energy released from bond formation is greater than the energy absorbed breaking the original bonds

Question 5

define endothermic

Answer 5

heat energy is absorbed
the energy absorbed breaking the original bonds is greater than energy released forming new bonds

Question 6

define activation energy and what way does the arrow face on an energy profile

Answer 6

the minimum energy required for a chemical reaction to take place
always up

Question 7

what are standard conditions and standard state

Answer 7

298K and 1 atm and 1 moldm^-3
the physical state of elements under standard conditions

Question 8

define enthalpy

Answer 8

heat content stored in a chemical system

Question 9

define enthalpy change

Answer 9

the heat exchanged with the surroundings during a chemical reaction
the difference between the enthalpy of the products and the reactants

Question 10

what is the equation for energy change

Answer 10

Q = MCΔT

Question 11

how do you work out enthalpy change from energy change

Answer 11

ΔH = Q/n

Question 12

define enthalpy change of neutralisation

Answer 12

the enthalpy change when 1 mol of water is formed from a neutralisation reaction under standard conditions and all reactants and products are in standard state

Question 13

what are the causes for less energy bring transferred than expected when working out enthalpy change of combustion

Answer 13

heat loss to surroundings
incomplete combustion
evaporation
non-standard conditions

Question 14

what is the value of enthalpy change of neutralisation

Answer 14

-57.5kJmol

Question 15

define average bond enthalpy

Answer 15

energy required to break 1 mol of a specified type of bond in a gaseous molecule

Question 16

what are the properties of bond enthalpy

Answer 16

energy is always required to break bonds]always positive and always have a positive enthalpy value

Question 17

what kind of energy and enthalpy change are bond formation

Answer 17

exothermic and releases energy

Question 18

what is Hess’s Law

Answer 18

If a reaction can take place by more than one route, the initial and final concentrations are the same and the total energy change is the same for each route

Question 19

what is reaction rate

Answer 19

the change in concentration of a reactant/product in a given time

Question 20

what makes an effective collision

Answer 20

sufficient speed and correct orientation

Question 21

whta factors can change rate of a chemical reaction

Answer 21

concentration
temperature
pressure
use of a catalyst
surface area of solid reactants

Question 22

what effect does increasing pressure have on reactants and why

Answer 22

increases rate
particles have more energy so there are more frequent successful collisions and therefore an increased rate

Question 23

what is the rule of thumb for reaction rate and temperature

Answer 23

a 10 degree increase in temperature doubles the rate

Question 24

what effect does increasing concentration/pressure have on rate of reaction

Answer 24

increases rate as there are more particles per unit of volume which leads to more successful and frequent collisions and therefore an increased rate

Question 25

how can progress of a chemical reaction be followed

Answer 25

monitoring removal of a reactant/formation of a product

Question 26

what 2 ways are there to determine rate of reaction when gas is produced

Answer 26

monitoring volume of gas produced or loss of mass of reactants

Question 27

what does a catalyst do

Answer 27

increase rate of reaction by lowering activation energy by offering a lower reaction pathway leading to more particles exceeding activation energy is not used up in the reaction/is regenerated at the end

Question 28

what is a homogenous catalyst

Answer 28

catalyst that is in the same state as the reactants

Question 29

how does a homogenous catalyst interact with reactants

Answer 29

forms an intermediate which breaks down to give the product and regenerates the catalyst

Question 30

give 2 examples of homogenous catalysts

Answer 30

sulfuric acid - production of esters chlorine radicals in zone repletion

Question 31

what is different about the equilibrium constant to regular constants

Answer 31

only constant at a given temperature

Question 32

how does a Boltzmann distribution model show the effects of a catalyst

Answer 32

Ea is lower than normal so a greater proportion of particles exceed the lower Ea

Question 33

what is Le Chatelier's principle

Answer 33

when a system in dynamic equilibrium experiences an external change, equilibrium will shift to minimise the effect

Question 34

does a catalyst have an effect on equilibrium

Answer 34

no

Question 35

How is Kc worked out in aA + bB -> cC + dD

Answer 35

[C]c x [D]d / [A]a x [B]b

Question 36

what is an autocatalysis

Answer 36

a reaction product that acts as a catalyst for that reaction

Question 37

what are the main features of a Boltzmann Distribution model

Answer 37

no molecules have 0 energy no maximum energy area under curved is equal to the number of molecules/particles

Question 38

how does a Boltzmann Distribution curve change when temperature increases

Answer 38

peak is lower and shifted to the right, a greater proportion of molecules can exceed Ea

Question 39

what are the main properties of a catalyst

Answer 39

not used up in a reaction regenerated at the end of a reaction may react with reactant to form an intermediate and provide a surface for the reaction to take place on

Question 40

what is dynamic equilibrium

Answer 40

when the rate of the forwards reaction equals the rate of the backwards reaction at the same time in a closed system where the concentration of reactants and products remain constants

Question 41

what are the benefits of using a catalyst

Answer 41

lowers Ea less electricity is used product is made faster and cuts costs and increases profits

Question 42

what is a heterogenous catalyst

Answer 42

a catalyst that is in a different state to the reactants

Question 43

how does a heterogenous catalyst interact with reactants

Answer 43

usually solids in contact with gaseous reactants / reactants in solution reactants are adsorbed onto the surface where the reaction takes place after the reaction, products leave via desorption

Question 44

give examples of a heterogenous catalyst

Answer 44

iron in the haber process nickel - hydrogenation of alkenes