P2 ADD MORE 3a energetics

Question 1

what is an exothermic reaction?

Answer 1

in exothermic reactions the temp of the surroundings increases and the heat content of the system falls, so in other words it releases heat energy

Question 2

what is an endothermic reaction?

Answer 2

when the temp of the surroundings falls and the heat content of the system increases, in other words it takes in heat energy

Question 3

what type of reaction is a neutralisation reaction?

Answer 3

give energy out so exothermic

Question 4

what type of reaction is a displacement reaction?

Answer 4

they can be both exo and endo - thermic

Question 5

what type of reaction is a combustion reaction?

Answer 5

give energy out so exothermic

Question 6

what is calorimetry?

Answer 6

a technique used to measure changes in enthalpy of chemical reactions

Question 7

what are the two types of calorimetry experiments?

Answer 7

enthalpy changes of reactions in solution

enthalpy changes of combustion

Question 8

what is the energy profile like for an exothermic reaction?

Answer 8

products have less energy than the reactants (transfer to surroundings)
- the energy transferred to the surroundings is the difference between the reactants the the
products
- arrow points downward

Question 9

what is the energy profile like for an endothermic reaction?

Answer 9

products have more energy than the reactants
- again the difference between the products and the reactants show the amount of energy being taken in
arrow points up

Question 10

what is the peak mean in the energy profiles?

Answer 10

activation energy

- this is the minimum amount of energy needed for particles to react

Question 11

how do you calculate the activation energy on an energy profile?

Answer 11

its from the reactants to the peak

- on an endothermic one it’ll be much greater

Question 12

what type of energy change will be shown as negative?

Answer 12

exothermic because the energy has been transferred from the chemicals to the surroundings

Question 13

what type of energy is required to break a bond?

Answer 13

endothermic

Question 14

what type of energy is required to make a bond?

Answer 14

exothermic

Question 15

how do you calculate energy changes?

Answer 15

find the bonds
when breaking bonds (first part of equation) add bonds together
on the other side of the equation bonds are made so it has to be a negative number
- remember to multiply depending on the number in front of it
put the negative one below the positive number and find the sum

Question 16

what is calorimetry suitable for?

Answer 16

reactions such as dissolving, displacement and neutralisation

Question 17

what assumptions are made about the experiment?

Answer 17

• the specific heat capacity of the solution is the same as pure water (4.18)
• that the density is the same as pure water
• the specific heat capacity of the container is ignored
• reaction is complete
• there are negligible heat losses

Question 18

what can a calorimeter be made up of?

Answer 18

polystyrene drinking cup, a vacuum flask or a metal can

Question 19

what type of reaction are salts dissolving in water?

Answer 19

either be exothermic or endothermic

Question 20

enthalpy of combustion experiment?

Answer 20

• a fixed volume of water is measured and transferred to the Copper can
• the spirit burner is weighed
• the initial temp of the water is measured and recorded
• the alcohol is ignited and the water is stirred constantly
• when the temp has risen by about 20 degrees the flame is extinguished that the spirit burner is re-weighed
• the final temp of the water is recorded

Question 21

what are the sources of error?

Answer 21

• heat losses
• incomplete combustion
• some heat is lost to surroundings
• some heat is absorbed by the calorimeter

Question 22

reaction in solution experiment?

Answer 22

• a fixed volume of one reagent is added to the calorimeter and the initial temp is taken with a thermometer
• an excess amount of the second reagent is added and the solution is stirred continuously
• the max temp is recorded and the temp rise is calculated

Question 23

what is the equation of calculating energy transferred in a calorimeter?

Answer 23

q = m x c x temperature change

Question 24

how do you find molar enthalpy change?

Answer 24

molar enthalpy change = heat change for the reaction / number of moles

Question 25

what is the energy change in an exothermic reaction?

Answer 25

the energy change is negative

Question 26

what is the energy change in an endothermic reaction?

Answer 26

the energy changes positive

Question 27

calorimetry investigation for displacement, dissolving and neutralisation?

Answer 27

• using a measuring cylinder put 25cm3 of NaOH solution into the calorimeter
• measure and record the temperature of the solution
• add 5cm3 of the dilute HCL and stir
• measure and record the highest temperature reached by the mixture
• repeat and increase the acid added by 5cm3 each time

Question 28

what happens when increasing the temperature in a reversible reaction?

Answer 28

it will cause the forward reaction to occur, increasing amount of products or yield and decreasing reactants
- it moves in the direction of endothermic reaction and increasing it means it can absorb more heat

Question 29

what happens when decreasing the temperature in an reversible reaction?

Answer 29

the equilibrium moves in the direction of the exothermic reaction

• decrease the amount of products and increase reactants
• allows more heat to be given off

Question 30

what happens if the pressure is increased in a reversible reaction?

Answer 30

the position of the equilibrium moves in the direction of the fewest moles of gas, more of the opposite side is produced

Question 31

what happens if the pressure is decreased in a reversible reaction?

Answer 31

it causes the position of move to the side with the most moles, and it will produce less of that same side