Enthaply changes

Question 1

What is the law of the conservation of energy?

Answer 1

Energy cannot be created or destroyed, just converted from one form to another.

Question 2

Define enthalpy

Answer 2

The heat content that is stored in a chemical system.

Question 3

Define enthalpy change

Answer 3

The heat exchanged with the surroundings during a chemical reaction.

The difference between the enthalpy of the products and the reactants.

Question 4

Define exothermic

Answer 4

A reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings.

Question 5

Define endothermic

Answer 5

A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat beaing taken out of the surroundings.

Question 6

Define activation energy

Answer 6

The minimum energy required for a reaction to take place.

Question 7

is exothermic postitive or negative?

Answer 7

negative, Enthalpy of reactants > Enthalpy of products

Question 8

is endothermic postitive or negative?

Answer 8

postitive, Enthalpy of reactants < Enthalpy of products

Question 9

How to rememeber what is bond breaking or making

Answer 9

BendoMexo

Question 10

is exothermic bond breaking or making?

Answer 10

Making

Question 11

is endothermic bond breaking or making?

Answer 11

Breaking

Question 12

if Activation energy is large, what does this mean for bond strength and the rxn

Answer 12

Strong bonding

Slower reaction

Question 13

if Activation energy is small, what does this mean for bond strength and the rxn

Answer 13

Weak bonds

Fast reaction

Question 14

what must you do when drawing out enthaply diagrams?

Answer 14

State symbols
Label axis
Enthalpy change
Activation energy

Question 15

Draw an exothermic enthaply diagram

Answer 15

look at notes

Question 16

Draw an endothermic enthaply diagram

Answer 16

look at notes

Question 17

Is an endothermic or exothermic reaction more likely to happen?

Answer 17

Exothermic

Question 18

What is the heat given out equation equation?

Answer 18

Q = m c ΔT

Question 19

What does ‘Q’ stand for in Q = m c ΔT

Answer 19

energy change with surroundings (J)

Question 20

What does ‘m’ stand for in Q = m c ΔT

Answer 20

mass of water in grams, cm^3

Question 21

What does ‘c’ stand for in Q = m c ΔT

Answer 21

specific heat capacity of water, 4.18 H g^-1 K^-1

Question 22

What does ‘ΔT’ stand for in Q = m c ΔT

Answer 22

Change in temperature

Question 23

What is the enthaply change equation?

Answer 23

• Q/mol

Question 24

Define standard enthalpy change of reaction

Answer 24

The enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, with all reactants and products in their standard states.

Question 25

What are the standard conditions?

Answer 25

Standard pressure - 1 atm Standard temperature - 298K Standard concentration - 1mol/dm^3 Standard state - The physical state of a substance under standard conditions

Question 26

Define standard enthalpy change of formation

Answer 26

The enthalpy change that takes place when one mole of a compound is formed from its constituent elements under standard conditions, with all reactants and products in their standard states.

Question 27

what is an example of enthaply change of formation?

Answer 27

S (s) + Cl2 (g) ----> SCl2 (l)

Question 28

what is one mole of product produced in?

Answer 28

enthalpy change of formation

Question 29

Define standard enthalpy change of combustion

Answer 29

The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, with all reactants and products in their standard states.

Question 30

what is an example of enthalpy change of combustion

Answer 30

C9H20 (l) + 14O2 (g) --------> 9CO2 (g) + 10H2O (l)

Question 31

what is one mole of substance reacted in?

Answer 31

enthalpy change of combustion

Question 32

Define standard enthalpy change of neutralisation

Answer 32

The enthalpy change for the formation of one mole of water from the neutralisation of an acid and a base, under standard conditions, with all reactants and products in their standard states.

Question 33

what is an example of enthalpy change of neutralisation

Answer 33

HCl + NaOH ------> NaCl + H2O

Question 34

what is one mole of water produced in?

Answer 34

enthalpy change of neutralisation

Question 35

Method to work out the enthaply change of neutralisation

Answer 35

1. Allow acid and the base solutions to equilibrate 2. Using the measuring cylinder, pour 25cm^3 of the base solution into a polystyrene cup 3. Measure and record the temperature of the soltution in the polystyrenme cup to a suitable accuracy 4. Using a measuring cylinder again add 25cm^3 of the acid to the polystyrene cup mixing gently 5. Observe the increase in temperature of the solution ajnd record the maximum temperature reached to a suitable reaction

Question 36

how to improve the method to work out the enthaply change of neutralisation

Answer 36

better insulation of the polystyrene cup (add a lid) | Use a cooling curve

Question 37

What are the causes for less energy being transferred than expected when working out ΔH(c)?

Answer 37

Heat loss to the surroundings Incomplete combustion Non-standard conditions

Question 38

How can heat loss be accounted for using a graph of temperature against time?

Answer 38

Extrapolate the cooling curve back to when it was added.

Question 39

how to calculate deviation

Answer 39

(100) x (| Actual value - expected value |) --------------------------------------------------------------- (| expected value |)

Question 40

how to decrease percentage error

Answer 40

more precise thermometer repeates and mean add a lid to reduce heat loss

Question 41

what is average bond enthaply?

Answer 41

the enthaply change that takes place when one mole of a particular of bond in a gaseous molecule is broken. it is endothermic

Question 42

how to work out bond ethalpy change?

Answer 42

ΔH = reactant enthaply - product enthalpy

Question 43

What are some properties of bond enthalpies?

Answer 43

Energy is always required to break bonds Bond enthalpies are always endothermic Bond enthalpies always have a positive enthalpy value

Question 44

What kind of energy and enthalpy changes are bond formation?

Answer 44

Exothermic and releases energy

Question 45

What is Hess' law?

Answer 45

If a reaction can take place by more than one route and the initial and final conditions are the same, the enthalpy change is the same for each route.

Question 46

What is Beckham's law?

Answer 46

The enthaply change of the reverse reaction has the same value, but the opposite sign.

Question 47

which way to the arrows point when using combustion hess cycles?

Answer 47

towards CO2 and H2O

Question 48

which way to the arrows point when using formation hess cycles?

Answer 48

away from elements

Question 49

formation equations

Answer 49

products - reactants

Question 50

combustion equation

Answer 50

reactants - products

Question 51

average bond enthalpy equations

Answer 51

reactants - products

Question 52

FOCI

Answer 52

FORMATION OUT COMBUSTION IN