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A Level Chemistry AQA: Physical > Energetics > Flashcards

Energetics Flashcards

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1
Q
  1. Define enthalpy change
A
  1. Enthalpy change is the amount of heat energy taken in or given out during any change in a system provided the pressure is constant
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2
Q
  1. What is an exothermic change?
A
  1. Energy is transferred from the system (chemicals) to the surroundings
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3
Q
  1. What is an endothermic change?
A
  1. energy is transferred from the surroundings to the system (chemicals).
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4
Q
  1. Define the standard enthalpy change of formation
A
  1. enthalpy change when 1 mole of the compound is formed from its elements under standard conditions (298K and 100kpa), all reactants and products being in their standard states
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5
Q
  1. Define the standard enthalpy change of combustion
A
  1. enthalpy change that occurs when one mole of a substance is combusted completely in oxygen under standard conditions. (298K and 100kPa), all reactants and products being in their standard states.
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6
Q
  1. State 4 factors which constitute standard conditions
A
  1. 100 kPa pressure; 298 K; Solutions at 1mol dm-3 ; all substances should have their normal state at 298
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7
Q
  1. What does incomplete combustion produce?
A
  1. Soot (carbon), carbon monoxide and water.
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8
Q
  1. What is ∆H for exothermic reactions?
A
  1. Negative
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9
Q
  1. What is ∆H for endothermic reactions?
A
  1. Positive
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10
Q
  1. What’s the equation for working out enthalpy change experimentally?
A
  1. energy change = mass of solution x heat capacity x temperature change
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11
Q
  1. What’s the unit of specific heat capacity?
A
  1. J g-1K-1
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12
Q
  1. What’s the units of temperature change?
A
  1. K
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13
Q
  1. With calorimetry, why is a polystyrene cup placed into a beaker?
A
  1. Insulation and support
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14
Q
  1. What do we do in calorimetry if it is difficult to obtain the final temperature?
A
  1. Take readings at regular time intervals and extrapolate the temperature curve/line back to the time the reactants were added together
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15
Q
  1. What are 4 errors in using the polystyrene cup method of calorimetry to measure the enthalpy change?
A
  1. Heat transfer from surroundings (usually loss); The method assumes all solutions have the heat capacity of water; neglecting the specific heat capacity of the calorimeter- we ignore any heat absorbed by the apparatus; reaction or dissolving may be incomplete or slow; Density of solution is taken to be the same as water
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16
Q
  1. What’s a simple method using calorimetry to measure the enthalpy of combustion?
A
  1. fuel is burnt and the flame is used to heat up water in a metal cup. H……..(NOT FINISHED)
17
Q
  1. How do you convert from J mol-1 to KJ mol-1?
A
  1. Divide by 1000
18
Q
  1. What does Hess’ Law state?
A
  1. The total enthalpy change for a reaction is independent of the route by which the chemical change takes place
19
Q
  1. What is the first law of thermodynamics?
A
  1. Energy is always conserved
20
Q
  1. What is the equation using Hess’ law to determine the enthalpy of combustion?
A
  1. ∑∆H c reactants- ∑∆Hc products
21
Q
  1. What is the equation using Hess’ law to determine the enthalpy of formation?
A
  1. ∑∆Hf products- ∑∆Hf reactants
22
Q
  1. Define the mean bond enthalpy
A
  1. enthalpy needed to break the covalent bond into gaseous atoms, averaged over different molecules
23
Q
  1. What are the units of mean bond enthalpy?
A
  1. kJ mol-1
24
Q
  1. What’s the equation for working out the mean bond enthalpy?
A
  1. ∆H = Σ bond energies broken - Σ bond energies made
25
Q
  1. Draw the bonds which make up carbon dioxide i.e. as a display formula
A
  1. O = C = O
26
Q
  1. Draw the bonds which make up water i.e. as a display formula
A

O
/ \
H H

27
Q
  1. Draw the bonds which make up oxygen i.e. as a display formula
A

O = O

28
Q
  1. How many bonds make up ethanol?
A

8

29
Q
  1. How many bonds make up propan-1-ol?
A

11

30
Q
  1. How many bonds which make up butan-1-ol?
A

14

A Level Chemistry AQA: Physical (12 decks)

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