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MPW chemistry > Enthaply changes > Flashcards

Enthaply changes Flashcards

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1
Q

What is the law of the conservation of energy?

A

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

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2
Q

Define enthalpy

A

The heat content that is stored in a chemical system.

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3
Q

Define enthalpy change

A

The heat exchanged with the surroundings during a chemical reaction.

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

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4
Q

Define exothermic

A

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

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5
Q

Define endothermic

A

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.

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6
Q

Define activation energy

A

The minimum energy required for a reaction to take place.

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7
Q

is exothermic postitive or negative?

A

negative, Enthalpy of reactants > Enthalpy of products

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8
Q

is endothermic postitive or negative?

A

postitive, Enthalpy of reactants < Enthalpy of products

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9
Q

How to rememeber what is bond breaking or making

A

BendoMexo

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10
Q

is exothermic bond breaking or making?

A

Making

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11
Q

is endothermic bond breaking or making?

A

Breaking

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12
Q

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

A

Strong bonding

Slower reaction

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13
Q

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

A

Weak bonds

Fast reaction

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14
Q

what must you do when drawing out enthaply diagrams?

A

State symbols
Label axis
Enthalpy change
Activation energy

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15
Q

Draw an exothermic enthaply diagram

A

look at notes

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16
Q

Draw an endothermic enthaply diagram

A

look at notes

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17
Q

Is an endothermic or exothermic reaction more likely to happen?

A

Exothermic

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18
Q

What is the heat given out equation equation?

A

Q = m c ΔT

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19
Q

What does ‘Q’ stand for in Q = m c ΔT

A

energy change with surroundings (J)

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20
Q

What does ‘m’ stand for in Q = m c ΔT

A

mass of water in grams, cm^3

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21
Q

What does ‘c’ stand for in Q = m c ΔT

A

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

22
Q

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

A

Change in temperature

23
Q

What is the enthaply change equation?

A
  • Q/mol
24
Q

Define standard enthalpy change of reaction

A

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.

25
Q

What are the standard conditions?

A

Standard pressure - 1 atm
Standard temperature - 298K

Standard concentration - 1mol/dm^3
Standard state - The physical state of a substance under standard conditions

26
Q

Define standard enthalpy change of formation

A

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.

27
Q

what is an example of enthaply change of formation?

A

S (s) + Cl2 (g) —-> SCl2 (l)

28
Q

what is one mole of product produced in?

A

enthalpy change of formation

29
Q

Define standard enthalpy change of combustion

A

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.

30
Q

what is an example of enthalpy change of combustion

A

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

31
Q

what is one mole of substance reacted in?

A

enthalpy change of combustion

32
Q

Define standard enthalpy change of neutralisation

A

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.

33
Q

what is an example of enthalpy change of neutralisation

A

HCl + NaOH ——> NaCl + H2O

34
Q

what is one mole of water produced in?

A

enthalpy change of neutralisation

35
Q

Method to work out the enthaply change of neutralisation

A
  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
36
Q

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

A

better insulation of the polystyrene cup (add a lid)

Use a cooling curve

37
Q

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

A

Heat loss to the surroundings
Incomplete combustion
Non-standard conditions

38
Q

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

A

Extrapolate the cooling curve back to when it was added.

39
Q

how to calculate deviation

A

(| expected value |)

40
Q

how to decrease percentage error

A

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

41
Q

what is average bond enthaply?

A

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

42
Q

how to work out bond ethalpy change?

A

ΔH = reactant enthaply - product enthalpy

43
Q

What are some properties of bond enthalpies?

A

Energy is always required to break bonds
Bond enthalpies are always endothermic

Bond enthalpies always have a positive enthalpy value

44
Q

What kind of energy and enthalpy changes are bond formation?

A

Exothermic and releases energy

45
Q

What is Hess’ law?

A

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.

46
Q

What is Beckham’s law?

A

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

47
Q

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

A

towards CO2 and H2O

48
Q

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

A

away from elements

49
Q

formation equations

A

products - reactants

50
Q

combustion equation

A

reactants - products

51
Q

average bond enthalpy equations

A

reactants - products

52
Q

FOCI

A

FORMATION OUT COMBUSTION IN

MPW chemistry (14 decks)

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