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OCR Chemistry > 3.2 PHYSICAL CHEMISTRY > Flashcards

3.2 PHYSICAL CHEMISTRY Flashcards

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1
Q

Define chemical energy

A
  • The energy held within the bonds between atoms
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2
Q

Define enthalpy

A
  • A measure of the heat/thermal energy content of a substance
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3
Q

Define enthalpy change ∆H

A
  • The heat exchange with the surroundings during a chemical reaction
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4
Q

Define system and surroundings

A

System = the atoms and bonds in the chemical reaction
Surroundings = everything around

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5
Q

Describe the relationship between energy and system/surroundings

A
  • Heat/energy loss in a chemical system = heat/energy gain to the surroundings
  • Heat/energy gain in a chemical system = heat/energy loss to the surroundings
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6
Q

Draw a labled exothermic diagram for enthalpy change

A
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7
Q

Draw a labled endothermic diagram for enthalpy change

A
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8
Q

Describe the term exothermic reaction in three ways

A

1) Heat energy is given out to surroundings from chemical reaction
2) More energy is released when product bonds are formed than the energy absorbed when breaking the reactant bonds
3) The enthalpy of reactants higher than enthalpy of products (thus, negative value)

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9
Q

Is bond breaking an exothermic or endothermic process?

A
  • Endothermic
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10
Q

Is bond forming an exothermic or endothermic process?

A
  • Exothermic
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11
Q

State and lable the two equations needed to work out ∆H from heat energy

A
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12
Q

Define activation energy Eₐ

A
  • The minimum amount of energy required for a reaction to take place
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13
Q

Define calorimetry

A
  • Working out the enthalpy change of a reaction
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14
Q

State what is measured during calorimetry to determine enthalpy change

A
  • The temperature change of a chemical system (the reaction)
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15
Q

Conclude the type of reaction if a temperature rise is detected during calorimetry

A
  • The reaction is exothermic
  • Heat energy has been released to the surroundings
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16
Q

Conclude the type of reaction if a temperature drop is detected during calorimetry

A
  • The reaction is endothermic
  • Heat energy has been taken in from the surroundings
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17
Q

State the equation used after calorimetry

A
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18
Q

State why a polystyrine cup is used in a beaker during calorimetry

A
  • Polystyrine acts as an insulator to reduce heat loss by evapourisation
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19
Q

Draw and lable a graph for calorimetry

A
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20
Q

Describe the term copper calorimetry for combustion enthalpy

A
  • When the heat energy from the combustion of a fuel is used to increase the temperature of a known mass of water
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21
Q

State the three reasons why experimental values differ from data values for combustion enthalpy

A

1) Non-standard conditions (298K 100kPa)
2) Incomplete combustion
3) Potential heat loss to surroundings

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22
Q

Define average bond enthalpy

A
  • The energy needed to break 1 mole of gaseous bonds in GASEOUS MOLECULES to form gaseous atoms
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23
Q

State why bond enthalpy
values are always positive

A
  • Because bond breaking is an endothermic process
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24
Q

Describe what a smaller bond enthalpy indicates about that bond

A

Smaller bond enthalpy = weaker bond = less energy to break = more reactive

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25
Q

State the equation for ∆Hᶠ in a chemical reaction

A
26
Q

State the equation for ∆Hᶜ in a chemical reaction

A
27
Q

Define standard enthalpy change of formation ∆Hᶠ

A
  • The enthalpy change when 1 mole of a compound is formed from its constituent elements under standard conditions
28
Q

Define standard enthalpy change of neutralisation ∆Hₙₑᵤₜ

A
  • The enthalpy change when 1 mole of water is formed from a neutralisation reaction under standard conditions
29
Q

Define standard enthalpy change of combustion ∆Hᶜ

A
  • The enthalpy change when 1 mole of a substance is completely combusted under standard conditions
30
Q

Draw an enthaply change of reaction from enthalpy change of combustion

A
31
Q

Draw an enthaply change of reaction from enthalpy change of formation

A
32
Q

State why initial rate (T=0) has the highest rate of reaction

A
  • Because concentrations of reactants are highest at the start of a reaction
  • Gradient of tangent to the curve is also steepest here
33
Q

State and describe the five factors that affect the rate of reaction

A

1) Temperature (↑ temp = ↑ rate)
2) Pressure (for gases) (↑ pressure = ↑ rate)
3) Concentration (↑ conc = ↑ rate)
4) Surface area (↑ SA = ↑ rate)
5) Catalyst (+ cat = ↑ rate)

34
Q

State in terms of collision theory the effect of these factors (except catalysts) on the rate of reaction

A
  • They ensure that particles collide with sufficient energy to overcome activation energy frequently
  • Thus, ROR increases
35
Q

State the equation for rate of reaction

A
36
Q

State the units for rate of reaction

A

mol dm⁻³ s⁻¹

37
Q

State the three ways in which changing quantitys can be measured for rate of reaction

A

1) Concentration of a reactant or product (titration)
2) Gas volumes of products (gas syringe)
3) Mass of products forming/decreasing mass of reactants (balance)

38
Q

State the equation for rate of reaction on a graph

A
39
Q

Describe how to determine rate of reaction from a graph

A

1) Draw a tangent to the curve wherever required
2) Use the formula gradient=∆y/∆x

40
Q

Define catalyst

A
  • Increase the rate of a reaction without being used up by the overall reaction
  • Allows the reaction to proceed via a different route by lowering activation energy
41
Q

State and explain the two types of catalysts

A

1) Homogenous catalysts (where the catalyst and reactants are in the same phase/state)
2) Heterogenous catalysts (where the catalyst and reactants are in the different phase/state)

42
Q

Describe the two benefits of using catalysts

A

1) Reduces the energy demand from combustion of fossil fuels
2) Increases economic sustainability because it lowers temperatures

43
Q

Explain what the boltzmann distribution shows

A
  • The distribution of energies of particles at a particular temperature
  • The proportion of particles with sufficient energy to overcome activation energy
44
Q

Draw and lable a generic boltzmann distribution and state the features

A
45
Q

Explain the effect of temperature on reaction rate via a labled boltzmann distribution

A
46
Q

Explain the effect of catalysts on reaction rate via a labled boltzmann distribution

A
47
Q

State the three features required for an equilibrium to be dynamic

A

1) Closed system
2) Concentrations of reactants and products remaining constant
3) Rate of forward and backward reactions to be equal

48
Q

State the three features that affect position of equilibrium

A

1) Temperature
2) Gaseous pressure
3) Concentration

49
Q

Explain fully the effect of changing concenteration on equilibrium position

A
50
Q

Explain fully the effect of changing gaseous pressure on equilibrium position

A
51
Q

Explain fully the effect of changing temperature on equilibrium position

A
52
Q

State why catalysts do not affect the position of equilibrium

A
  • Because they speed up the rate of the foward and backward reaction by equal amounts
53
Q

Describe industrial conditions

A
  • They tend to be a comprimise between rate of reaction and yeild of production (equilibrium position)
  • To ensure profits while still being safe
54
Q

Draw a concentration-time graph identifying dynamic equilibrium of reactants and products when equilibrium lies to the LEFT

A
55
Q

Draw a concentration-time graph identifying dynamic equilibrium of reactants and products when equilibrium lies to the RIGHT

A
56
Q

Draw a concentration-time graph identifying dynamic equilibrium of reactants and products when equilibrium lies in the MIDDLE

A
57
Q

Define homogenous equilibrium

A
  • Where all species are in the same phase/state
58
Q

State the equilibrium constant Kc expression

A
59
Q

State what is meant is equilibrium constant Kc has a value of 1

A
  • Equilibrium lies in the MIDDLE of reactants and products
60
Q

State what is meant is equilibrium constant Kc has a value bigger than 1

A
  • Equilibrium lies to the RIGHT
  • (Products/forward is favoured)
61
Q

State what is meant is equilibrium constant Kc has a smaller than 1

A
  • Equilibrium lies to the LEFT
  • (Reactants/backwards is favoured)
62
Q

State the units of equilibrium constant Kc

A

mol dm⁻³

OCR Chemistry (13 decks)

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