3.2

Question 1

define enthalpy

Answer 1

the thermal energy stored in a chemical system. we can measure this by seeing if the temp of a reaction changes

Question 2

how you know a Reaction has taken place

Answer 2

color change, effervescence, precipitate formed, temp/energy change

Question 3

exothermic reactions

Answer 3

give out energy to their surroundings, make things feel hot, the energy of the products is less than that of the reactants

Question 4

endothermic reactions

Answer 4

take in energy form their surroundings, make things feel cold, the energy of the products is greater than that of the reactants

Question 5

activation energy

Answer 5

the energy needed to start breaking the bonds in the reactants. the minimum energy needed for a reaction to take place

Question 6

how to calculate enthalpy change

Answer 6

enthalpy to break bonds - enthalpy to make bonds

Question 7

negative enthalpy change means the reaction is

Answer 7

exothermic

Question 8

positive enthalpy change mean the reaction is

Answer 8

endothermic

Question 9

enthalpy change of neutralisation

Answer 9

(delta H neut) enthalpy change when one mole of water is formed from a neutralisation reaction can be exothermic or endothermic

Question 10

enthalpy change of formation

Answer 10

(delta H f) enthalpy change when one mole of a compound is formed from its elements in their standard state usually exothermic

Question 11

enthalpy change of combustion

Answer 11

(delta H c) enthalpy when one mole of a substance reacts completely with O2 always exothermic

Question 12

standard conditions for enthalpy changes of reactions

Answer 12

pressure- 100 kPa (1 atm)

room temp- 289k (25`c)

Question 13

measuring enthalpy change experimentally

Answer 13

Q=mcT 
T=temp change
c=specific heat capacity of substance being heated
m= mass of object being heated
Q=heat lost or gained from reaction in J

Question 14

Hess’s law

Answer 14

The total enthalpy change of a reaction is independent of the route by which the reaction takes place provided the initial and final condition are the same

Question 15

to increase the rate of reaction

Answer 15

increase pressure, increase surface area, increase temp, add a catalyst, increase concentration, increase surface area

Question 16

why increase surface area

Answer 16

after rate of reaction as more particles are exposed and able to react

Question 17

why use a catalyst to increase rate of reaction

Answer 17

lowers the activation energy

Question 18

why increase the concentration

Answer 18

more particles per unit volume increase the chances go a successful collision

Question 19

rate of reaction

Answer 19

change in concentration of x over time

Question 20

two types of catalysts

Answer 20

heterogeneous catalyst, homogenous catalyst

Question 21

heterogenous catalyst

Answer 21

catalyst is in a different phase to the reactants i.e. solid catalyst vs gaseous reactants

Question 22

homogeneous catalyst

Answer 22

catalyst is in the same phase as the reactants i.e. all liquid or gaseous

Question 23

benefits of catalysts in general

Answer 23

increase sustainability, reduce temp needed -> cheaper

Question 24

Botzmann distribution

Answer 24

shows the distribution of molecules of certain energies, area under the curve= no. pf molecules in the system, if the temp is increased the curve becomes broader and flatter

Question 25

Le Chateliers principle

Answer 25

if conditions change the position of the equilibrium will respond by also changing to minimise the change imposed

Question 26

factors affecting the position of the equilibrium

Answer 26

concentrations reactants of products, pressure, temperature

Question 27

how concentration affects the equilibrium position

Answer 27

if the either the products or reactants concentrations are changed the rate of the forwards/backwards reaction will increase to minimise the change

Question 28

how pressure affects the equilibrium position

Answer 28

increasing the pressure favours the side with the lease moles

Question 29

how temperature affects the equilibrium position

Answer 29

one of the reactions (forward or backwards) will be exothermic and the other endothermic increasing temp favours the endothermic reaction, decreasing it the exothermic reaction

Question 30

equilibrium constant kc

Answer 30

kc>1 equilibrium to the right kc<1 to the left

Question 31

how to calculate the equilibrium constant

Answer 31

concentrations of products to the power of no. of moles divided by concentrations of reactants to the power of no. of moles