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Chemistry GCSE > Energy and Equilibria > Flashcards

Energy and Equilibria Flashcards

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1
Q

Exothermic

A

Temperature increases, enthalpy decreases

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2
Q

Endothermic

A

Temperature decreases, enthalpy increases

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3
Q

Enthalpy

A

Chemical potential energy, measured in joules (J)

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4
Q

Examples of exothermic reactions

A
  1. Neutralisation

2. Acid + metal reactions

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5
Q

An example of an endothermic reaction

A

Thermal decomposition

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6
Q
  1. How can enthalpy change be expressed in terms of bond energies?
  2. Which values represent an endothermic reaction?
  3. Exothermic?
A
  1. Bonds broken - bonds made
  2. Positive
  3. Negative
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7
Q
  1. The breaking of bonds is:

2. The making of bonds is:

A
  1. Endothermic

2. Exothermic

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8
Q

Steps to calculate enthalpy change of a reaction

A
  1. Balance the equation
  2. Show all the bonds
  3. Show all bond energies
  4. Add the bond energies together
  5. ∆H = bonds broken - bonds made
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9
Q

What is the unit for bond energies?

A

kJ/mol

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10
Q

Equation for enthalpy released

A

Energy released = mass of liquid * specific heat capacity * change in temperature
OR
Q = m * c * ∆T

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11
Q

What is:

  1. The mass of 100ml of water?
  2. Water’s specific heat capacity*?

*Don’t need to know

A
  1. 100g

2. 4.18 kJ/kg/°C

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12
Q

Energy released per gram of fuel

A

= Enthalpy / mass of fuel

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13
Q

Calorimetry experiment steps

A
  1. Cold water is measured into a copper calorimeter (small metal cup)
  2. Starting temperature of the water is recorded using a thermometer
  3. The water is heated using the flame from the burning fuel
  4. The final temperature of the water is recorded
    THEN Q = mc∆T

To find the mass of fuel burned, weigh the spirit burner before and after the experiment

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14
Q

What must be kept the same in the calorimetry experiment to ensure a fair test?

A
  1. Mass of water
  2. Distance between spirit burner and calorimeter
  3. Concentration of fuel
  4. Starting temperature of the water
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15
Q

How can you tell if a temperature change reaction is complete?

A

The reaction should have reached a minimum temperature

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16
Q

Reversible reaction

A

A reaction where the reactants form products, which, in turn, react together to form the reactants again

17
Q

What symbol indicates a reversible reaction?

A

⇌

18
Q

Examples of reversible reactions

A
  1. Blue copper (II) sulphate crystals ⇌ white anhydrous copper (II) sulphate
    - when heating the former, the crystals turn into white powder and the water driven off
    - loss of water of crystallisation takes place
  2. Ammonium chloride ⇌ ammonia + hydrogen chloride
    - when heating the former, white crystals appear further up test tube
    - recombination takes place further up, where it is cooler
19
Q

Dynamic equilibrium

A

When the forwards and backwards reactions take place at the same rate, meaning that there is no net change in the ratio of reactants and products

20
Q

Le Chatelier’s Principle

A

For any change imposed on an equilibrium, the position of the equilibrium will move to oppose that change

21
Q

What are the 3 things you can alter to change the position of equilibrium?

A
  1. Concentration
  2. Temperature
  3. Pressure
22
Q

What happens if you increase the concentration of the reactants?

A
  1. Increase concentration of reactants
  2. System opposes change
  3. Forwards reaction occurs more frequently
  4. Equilibrium shifts to the right
  5. Yield of products increases
23
Q

What happens if you decrease the concentration of the reactants?

A
  1. Decrease concentration of reactants
  2. System opposes change
  3. Backwards reaction occurs more frequently
  4. Equilibrium shifts to the left
  5. Yield of reactants increases
24
Q

What happens if you increase the temperature and the forwards reaction is exothermic?

A
  1. Increase temperature
  2. System opposes change
  3. Backwards reaction (endothermic - takes up heat) occurs more frequently
  4. Equilibrium shifts to the left
  5. Yield of reactants increases
25
Q

What happens if you decrease the temperature and the forwards reaction is endothermic?

A
  1. Decrease temperature
  2. System opposes change
  3. Backwards reaction (exothermic - gives off heat) occurs more frequently
  4. Equilibrium shifts to the left
  5. Yield of reactants increases
26
Q

What happens if you increase the pressure and the products have more molecules?

A
  1. Increase pressure → volume decreased
  2. System opposes change
  3. Equilibrium shifts to left (side with fewer molecules)
  4. Yield of reactants increases
27
Q

What happens if you decrease the pressure and the products have fewer molecules?

A
  1. Decrease pressure → volume increased
  2. System opposes change
  3. Equilibrium shifts to left (side with more molecules)
  4. Yield of reactants increases
28
Q

What effect does the addition of a catalyst have on the yield of products and reactants?

A

Nothing - catalysts only affect the rate of reaction

Chemistry GCSE (4 decks)

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