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Dynamic equilibria, chemical cells and fuel cells GapFill

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4-5
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A system in dynamic equilibrium, such as the reversible reaction to form ammonia from hydrogen and nitrogen in the  Le ChatelierAvogadroElectrolysisHaber process, will act to minimise a change in conditions.

  • If the concentration of a reactant or product is changed, the  statetemperatureconcentrationenergy level of all the substances will change until the reaction is at equilibrium again.
  • If the temperature of the system is changed, the rate of the forward and backward reactions will change until equilibrium is reached.  HighStableVariableRoom temperatures favour endothermic reactions, and  boilinglowstablevariable temperatures favour exothermic reactions.
  • For reactions with gaseous reactants, the pressure can affect the position of equilibrium. High pressures shift the position of equilibrium to the side with fewer  largegaseousliquidsolid molecules.
  • Catalysts do not change the position of equilibrium, but will speed up the rate at which it is reached.
When two connected metals with different reactivities are placed in an electrolyte,  a simple cella magneta catalystan electrolysis set-up is made. If these are placed in series,  an alkalia batteryan electrolytea fuel cell is formed, which provides a higher  chargetemperatureratevoltage than a single cell.

An chemical cell produces a voltage until the chemicals are  used upsolidifiedcooledgases

Fuel cells use a fuel such as hydrogen. They also take in  oxygennitrogenmethaneneon from the air. In these cells, hydrogen is  generatedpolymerisedoxidisedreduced to form  wateran alkalian acida carbohydrate as the only product. This reaction produces  a magnetic polea change in pressurea potential differencean increase in entropy. The half-equations for an electrochemical cell are:

  • Cathode: H2 (g) →  2H⁺4H⁺2OH⁻4OH⁻ (aq) + 2e⁻
  • Anode: 4H⁺ (aq) + O2 (g) +  3e⁻4OH⁻ (aq)4e⁻2e⁻ → 2H2O (l)

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Pass Mark
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