1.7 Simple Equilibria and Acid-Base Reactions

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WJEC A-Level Chemistry

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30 Terms

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What is dynamic equilibrium?

when the rate of forward reaction equals the rate of reverse reaction

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What is homogenous equilibrium?

all products and reactants are in the same state

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What is a heterogenous equilibrium?

not all products and reactants are in the same state

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What is Le Chatelier’s principle?

if a change is introduced into a system in equilibrium, the system responds by opposing the change

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Factors affecting equilibrium

  • concentration

  • temperature

  • pressure

  • catalyst

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Cu2+ + 4Cl- ⇌ CuCl42-

blue + . ⇌ green

What is observed if the concentration of Cl- is increased?

  1. Cl- has been added so the system wants to decrease the amount of Cl-

  2. The rate of forward reaction increases

  3. Equilibrium shifts in favour of products

  4. A green colour is observed

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2SO2 + O2 ⇌ 2SO3

→ -ΔH exothermic

← +ΔH endothermic

What happens to amount of SO3 if temperature is increased?

  1. Temperature has been increased so the system wants to decrease the temperature

  2. The rate of reverse endothermic reaction increases

  3. Equilibrium shifts in favour of reactants

  4. Amount of SO3 decreases

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N2 + 3H2 ⇌ 2NH3

4 moles ⇌ 2 moles

What happens to amount of ammonia if pressure is increased?

  1. Pressure has been increased so the system wants to decrease the pressure

  2. The rate of forward reaction increases

  3. Equilibrium shifts in favour of products

  4. Amount of ammonia increases

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Effect of catalysts

  • no effect on position of equilibria

  • only reduces time of reaction

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Equilibrium constant formula

aA + bB ⇌ cC + dD = Kc = [C]c x [D]d

. [A]a x [B]b

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How to work out Kc units

knowt flashcard image
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What is an acid?

proton (H+) donor

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What is a base?

proton (H+) acceptor

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base vs alkali

base = insoluble, alkali = soluble base

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strong vs weak acid

an acid is stronger if it can dissociate completely

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_ oxide + acid → (acid+base)

salt + water

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_ hydroxide + acid → (acid+alkali)

salt + water

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_ carbonate + acid →

salt + water + carbon dioxide

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metal + acid →

salt + hydrogen

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What is an amphoteric nature?

a substance that can act as an acid or a base e.g. water

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What happens to pH if concentration increases?

pH decreases

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pH =

-log [H+]

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[H+] =

10-pH

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Haber process

  • makes ammonia (alkali)

  • N2 + 3H2 ⇌ 2NH3

  • exothermic, ΔH = -92 kjmol-1

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Haber process compromised conditions

  • 200 atm (expensive+dangerous if higher)

  • 450°C (reaction too slow if lower)

  • Fe catalyst

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Contact process

  • makes sulfuric acid

  • 2SO2 + O2 ⇌ 2SO3

  • exothermic, ΔH = -196 kjmol-1

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Contact process compromised conditions

  • 1-2 atm (expensive+dangerous if higher)

  • 400°C-450°C (reaction too slow if lower)

  • V2O5 catalyst

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pH of seawater

slightly alkaline

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How is pH of seawater maintained?

maintained by buffering action of dissolved carbon dioxide, hydrogencarbonate, and carbonate ion

  • resists change in pH

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Increasing CO2 affect on seawater

  • increasing concentration = decrease in pH

  • fears that increased acidity will be detrimental to marine life e.g. corals