energetics

Question 1

in an endothermic reaction,

Answer 1

energy is taken in from the surroundings

Question 2

in an exothermic reaction,

Answer 2

energy is released into the surroundings

Question 3

in an exothermic reaction, temperature of the surroundings

Answer 3

increases

Question 4

what are 2 examples of exothermic reactions

Answer 4

combustion and neutralisation

Question 5

in endothermic reactions, temperature of the surroundings

Answer 5

decreases

Question 6

what is an example of an endothermic reaction

Answer 6

thermal decomposition

Question 7

how do you remember if energy goes in or out in exo and endo reactions

Answer 7

EXO = EXits

ENDO- in

Question 8

what is the law of conservation of energy

Answer 8

energy cannot be created or destroyed but it can be transferred

Question 9

displacement reactions are endo or exo

Answer 9

can be both

Question 10

neutralisation reactions are endo or exo

Answer 10

always exothermic

Question 11

combustion reactions are endo or exo

Answer 11

always exothermic

Question 12

what are the 2 types of calorimetry experiments

Answer 12

enthalpy changes of reactions in solution
enthalpy changes for combustion

Question 13

to calculate the amount of energy produced by a chemical reaction in solutions what do we do

Answer 13

• measure the temperature change when the solutions are mixed together
• the solutions need to be mixed together in an insulated container to prevent heat loss

Question 14

the method for reactions in solutions can be used for (3)

Answer 14

• neutralisation reactions
• dissolving solids
• displacement reactions

Question 15

what is the specific heat capacity of water

Answer 15

4.2

Question 16

what is the density of water

Answer 16

1 g/cm³

Question 17

in calorimetry experiments, what do we take for granted / assumptions (4)

Answer 17

• the specific heat capacity of the solution is the same as pure water (4.2)
• density of solution is same as pure water (1 g/cm³)
• reaction is complete
• specific heat capacity of the container is ignored

Question 18

A calorimeter can be made up of and why

Answer 18

a polystyrene drinking cup, a vacuum flask or a metal can

because they’re insulating materials

Question 19

how do you carry out a simple calorimetry experiment

Answer 19

• have a polystyrene cup with a plastic lid to prevent heat loss
• add one reagent
• have a thermometer there and measure initial temperature
• add the second reagent and stir continuosly
• record the maximum temperature it reaches and record the rise
• record energy released using Q=mcΔT

Question 20

equation for energy released

Answer 20

Q = m x c x ΔT

Question 21

what does Q stand for and units of measurement

Answer 21

heat energy change, J

Question 22

what does m stand for and units of measurement

Answer 22

mass of the substance being heated, g

Question 23

what does c stand for and units of measurement

Answer 23

specific heat capacity, J/g/°C

Question 24

what does ΔT stand for and units of measurement

Answer 24

temperature change, °C

Question 25

principle of a combustion calorimetry experiment

Answer 25

to use the heat released by a combustion reaction to increase the heat content of water

Question 26

method for enthalpy of combustion

Answer 26

- fill copper calorimeter with 100cm³ of pure water - measure initial temp - weigh spirit burner - place spirit burner under calorimeter ( under specific distance) - light the spirit burner and leave for 2 mins - after 2 mins measure the final temp of the water - re-weigh the spirit burner

Question 27

In combustion calorimetry experiment the main sources of error are (2)

Answer 27

Heat losses Incomplete combustion

Question 28

difference between the combustion experiment and the neutralisation etc.. experiment

Answer 28

combustion requires a spirit burner to burn

Question 29

what is enthalpy

Answer 29

energy

Question 30

what is molar enthalpy change

Answer 30

heat energy change per mole of substance

Question 31

how do you calculate molar enthalpy change

Answer 31

ΔH= Q / n = heat energy change / number of moles

Question 32

molar enthalpy units

Answer 32

kJ/ mol

Question 33

enthalpy units

Answer 33

joules

Question 34

when calculating molar enthalpy change, what do you do to the enthalpy (Q) ( think of the units used)

Answer 34

need to divide by 1000, because molar enthalpy is measured in kilojoules while enthalpy is in joules

Question 35

moles can be figured out using 2 equations

Answer 35

mass / Mr concentration x volume

Question 36

in molar enthalpy change, if the temperature of solution or water increased then the ΔH will be positive or negative and what reaction will it be

Answer 36

ΔH will be negative exothermic reaction

Question 37

in molar enthalpy change, if the temperature of solution or water decreased then the ΔH will be positive or negative and what reaction will it be

Answer 37

ΔH will be positive will be an endothermic reaction

Question 38

for an energy level diagram for exothermic reactions, how will the reactant and product lines look

Answer 38

as energy is being released, the reactant will be higher than the products

Question 39

draw an exothermic energy level diagram

Answer 39

reactant will be higher than the products, add the arrow pointing down in the middle of then saying that energy is released

Question 40

for an energy level diagram for endothermic reactions, how will the reactant and product lines look

Answer 40

products will have more energy than the reactants so the line will be higher up

Question 41

draw an endothermic energy level diagram

Answer 41

reactant line will be low arrow be pointing up saying energy is absorbed product line will be high

Question 42

what are the two labels ( x and y) for an energy level diagram

Answer 42

energy - y progress of reaction - x

Question 43

when drawing energy level diagrams, should you state the name of the products and reactants on the line

Answer 43

YES

Question 44

bond breaking is an _______ reaction because

Answer 44

endothermic reaction, energy must be supplied to existing bonds in order to break them

Question 45

bond forming is a _______ reaction because

Answer 45

exothermic energy is released

Question 46

total change for enthalpy for a reaction can be calculated if we know

Answer 46

the bond energies of all the species involved

Question 47

enthalpy change calculation

Answer 47

energy taken in - energy given out

Question 48

each bond has a ___ energy

Answer 48

bond

Question 49

what are bond energies

Answer 49

amount of energy needed to break the bond or the amount of energy given out when the bond is formed

Question 50

for exothermic reactions, enthalpy change will be positive or negative why

Answer 50

negative product will have more energy than reactant

Question 51

for endothermic reactions, enthalpy change will be positive or negative why

Answer 51

positive product will have less energy than reactant

Question 53

an exothermic reaction will occur if ( bond energies)

Answer 53

more energy is released when new bonds are formed than what was needed to break them

Question 54

an endothermic reaction will occur if ( bond energies)

Answer 54

if the energy taken in to break the bonds exceeds the energy when new bonds are formed

Question 55

for salts dissolving (ammonium nitrate) would it be a endo or exo thermic reaction and why

Answer 55

endothermic because temperature decreases

Question 56

for salts dissolving (calcium chloride) would it be a endo or exo thermic reaction and why

Answer 56

exothermic because temperature increases

Question 57

for neutralisation reactions, is it endo or exothermic and why

Answer 57

exothermic because temperature increases

Question 58

for displacement reaction, is it endo or exo and why

Answer 58

exo because temp increases

Question 59

for combustion, is it endo or exo and why

Answer 59

exo because temp increases

Question 60

How would you measure temperature change in displacement?

Answer 60

Measure temp of metal salt solution, add metal, record temp change

Question 60

How would you measure temperature change in neutralisation?

Answer 60

Mix acid and alkali, record temp before and after mixing

Question 61

How would you measure temperature change when salt dissolves?

Answer 61

Measure temp of water, add salt, stir, record temp after dissolving

Question 62

How would you measure temperature change in combustion?

Answer 62

Burn fuel under water in a can, measure water temp before and after