Chemical Equilibrium and Le Chatelier's Principle
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Questions and Answers

The forward reaction of PCl3 and Cl2 producing PCl~5 is ______.

exothermic

Introducing more PCl~3 into the mixture will shift the equilibrium to the ______.

right

Increasing pressure will favor the side with the ______ number of molecules.

smaller

If the temperature is increased, the equilibrium will shift in the ______ direction.

<p>backward</p> Signup and view all the answers

The reaction between iron (III) chloride and potassium thiocyanate forms a ______ complex.

<p>red</p> Signup and view all the answers

Adding hydrochloric acid caused the red color to ______ as the equilibrium shifted.

<p>disappear</p> Signup and view all the answers

When potassium thiocyanate is added to the second tube, the red complex ______.

<p>reforms</p> Signup and view all the answers

Chemical equilibrium is a state of dynamic balance in a reversible reaction where the rate of the forward reaction is the same as the rate of the ______ reaction.

<p>backward</p> Signup and view all the answers

Ammonia is one of the most important chemicals manufactured by the ______.

<p>chemical industry</p> Signup and view all the answers

A reversible reaction is one in which the products react to give back the ______, meaning the reaction can go in both directions.

<p>reactants</p> Signup and view all the answers

Le Chatelier's Principle states that if a ______ is applied to a system at equilibrium, the system re-adjusts to relieve the stress applied.

<p>stress</p> Signup and view all the answers

An increase in pressure will favour the reaction that brings about a reduction in ______, shifting towards the side with the smaller number of molecules.

<p>volume</p> Signup and view all the answers

In the forward reaction of 2NO2(g) to N2O4(g), heat is given out, making it an ______ reaction.

<p>exothermic</p> Signup and view all the answers

A change in pressure affects only an equilibrium reaction that has unequal numbers of gaseous ______ and products.

<p>reactants</p> Signup and view all the answers

ΔH with a negative sign indicates that a reaction has given out ______.

<p>heat</p> Signup and view all the answers

A catalyst speeds up the rate at which ______ is reached but does not change the position of equilibrium.

<p>equilibrium</p> Signup and view all the answers

Ammonia is manufactured by reacting nitrogen with ______

<p>hydrogen</p> Signup and view all the answers

A pressure of approximately ______ atmospheres is used in the production of Ammonia

<p>200</p> Signup and view all the answers

The Haber process to maximize the yield of ammonia favors high ______ and low temperature

<p>pressure</p> Signup and view all the answers

Sulfuric Acid is manufactured by a process known as the ______ Process

<p>Contact</p> Signup and view all the answers

The equilibrium constant, Kc, represents the relationship between the concentrations of the ______ and products

<p>reactants</p> Signup and view all the answers

The products in the equilibrium constant expression are always written ______ the line

<p>above</p> Signup and view all the answers

A temperature of ______°C is the best temperature for the catalyst to work at in the Contact Process

<p>450</p> Signup and view all the answers

In the equilibrium expression, each species concentration is raised to the power of its ______ in the balanced equation

<p>coefficient</p> Signup and view all the answers

When a yellow solution of iron(III) chloride (FeCl3) and a colourless solution of potassium thiocyanate (KCNS) were mixed, a ______ colour appeared.

<p>red</p> Signup and view all the answers

The equilibrium constant (Kc) for the reaction was calculated to be ______.

<p>138.87</p> Signup and view all the answers

Changing the ______ has no effect on this equilibrium as it is an equilibrium in solution with no gases involved.

<p>pressure</p> Signup and view all the answers

The red colour faded when the test tube containing the equilibrium mixture was placed in an ______-water bath.

<p>ice</p> Signup and view all the answers

The addition of KCNS caused the concentration of Fe^3+^ ions to ______ as the reaction shifted forward.

<p>decrease</p> Signup and view all the answers

The equilibrium constant expression for the reaction is ______ = [$\frac{{[NH}{3}]^{2}}{{[N}{2][H}_{2}]^{3}}$]

<p>K<del>c</del></p> Signup and view all the answers

At a certain high temperature T, the equilibrium constant (Kc) value for the reaction is equal to [$______$]

<p>20.25</p> Signup and view all the answers

Le Châtelier's principle states that if a system at equilibrium is subjected to a ______, it tends to oppose the stress.

<p>stress</p> Signup and view all the answers

Increases in temperature cause the value of Kc to ______ for an exothermic reaction.

<p>decrease</p> Signup and view all the answers

The metals used as catalysts in catalytic converters include ______, palladium, and rhodium.

<p>platinum</p> Signup and view all the answers

Catalysis that occurs in catalytic converters is known as ______ catalysis.

<p>heterogeneous</p> Signup and view all the answers

One way that catalysts increase the rate of reaction is by lowering the ______.

<p>activation energy</p> Signup and view all the answers

A substance that could 'poison' the catalysts of the catalytic converter is ______ compounds.

<p>lead</p> Signup and view all the answers

Flashcards

Chemical Equilibrium

A state of balance in a reversible reaction where the forward and backward reaction rates are equal.

Reversible Reaction

A reaction that can proceed in both directions, forming products from reactants and vice-versa.

Le Chatelier's Principle

If a stress is applied to a system at equilibrium, the system will shift to relieve the stress.

Stress (in equilibrium)

A change in reaction conditions, like concentration, pressure, or temperature.

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Effect of Pressure Change (gases)

Increased pressure favors the side of the reaction with fewer gas molecules (smaller volume).

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Catalyst

Substance that speeds up the rate of a reaction but does not alter the position of equilibrium.

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Exothermic Reaction

A reaction that releases heat to the surroundings.

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Endothermic Reaction

A reaction that absorbs heat from the surroundings.

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Effect of adding PCl3 on PCl5 concentration

Adding more PCl3 shifts the equilibrium to the right, increasing the concentration of PCl5.

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Effect of increased pressure on PCl5 concentration

Increasing pressure shifts the equilibrium to the side with fewer moles of gas, increasing PCl5 concentration if the reaction has fewer gas moles on the product side.

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Effect of increased temperature on PCl5 concentration

Increasing temperature in an exothermic forward reaction shifts the equilibrium to the left, decreasing PCl5 concentration.

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Equilibrium shift (Fe3+ + SCN- ⇌ Fe(SCN)2+)

The adding of a reactant or product changes the position of the equilibrium to create a new equilibrium that minimizes the change.

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Haber Process

Industrial process to produce ammonia, a key fertilizer.

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Equilibrium Constant (Kc)

A numerical value that represents the ratio of product concentrations to reactant concentrations at equilibrium for a reversible reaction.

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Dynamic Equilibrium

Reaction is occurring in both directions, but the overall concentrations do not change.

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Effect of Temperature on Kc

Increasing temperature shifts equilibrium toward endothermic reaction, decreasing temperature shifts to exothermic reaction.

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Effect of Pressure on Kc

Pressure changes do not affect the value of Kc, it only affects the position of equilibrium.

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Catalytic Converters

Devices that use catalysts to reduce harmful emissions from car exhausts.

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Heterogeneous Catalysis

Catalysts are in a different phase than reactants.

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Ammonia Production

Ammonia is produced by reacting nitrogen gas with hydrogen gas.

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Haber Process Conditions

High pressure (approx. 200 atmospheres) and low temperature (approx. 200 °C) are optimal for maximum ammonia yield in the Haber process.

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Equilibrium Constant (Kc)

Kc is a constant representing the ratio of product concentrations to reactant concentrations at equilibrium.

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Equilibrium Constant Equation

Kc = [products]coefficient / [reactants]coefficient. Each concentration is raised to the power of its coefficient in the balanced equation

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Sulfuric Acid Production

Sulfuric acid is manufactured by the Contact Process, reacting sulfur dioxide with oxygen in the presence of a catalyst (V2O5).

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Contact Process Conditions

To produce sulfuric acid, a temperature of approximately 450 °C and slightly above atmospheric pressure are used.

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Kc Calculation

Calculate Kc by using the equilibrium concentrations of reactants and products.

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Effect of Adding Reactant

Adding more reactant to a system at equilibrium will shift the reaction forward to consume the added reactant.

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Effect of Temperature

Increasing temperature favors the endothermic reaction, while decreasing temperature favors the exothermic reaction.

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Study Notes

Chemical Equilibrium

  • Definition: Chemical equilibrium is a dynamic state in a reversible reaction where the forward and backward reaction rates are equal.
  • Reversible Reaction: A reaction where products can react to reform reactants.
  • Dynamic State: Reactants continuously form products, and products continuously form reactants.
  • Le Chatelier's Principle: If a stress is applied to a system at equilibrium, the system will shift to relieve the stress.
  • Stress: Changes in reaction conditions (concentration, pressure, temperature).

Le Chatelier's Principle Examples

  • Concentration: Increasing reactant concentration shifts equilibrium toward product formation. Decreasing product concentration has the same effect.
  • Pressure: Increasing pressure favors the side with fewer gas molecules. Decreasing pressure favors the side with more gas molecules.
  • Temperature: Endothermic reactions shift toward products with increased temperature. Exothermic reactions shift toward products with decreased temperature. The sign of ΔH indicated whether the reaction is exothermic (+ΔH) or endothermic (-ΔH).

Effect of Change of Pressure in Gaseous Reactions

  • Increasing pressure in a gaseous reaction shifts equilibrium toward the side with fewer gaseous molecules.
  • A change in pressure affects only reactions with unequal numbers of gaseous reactants and products.
  • The fewer gaseous molecules occupy less volume and help to relieve the pressure.

Equilibrium Constant (Kc)

  • Definition: Kc is a constant that represents the relationship between the concentrations of reactants and products at equilibrium.
  • The concentrations of products are written above the line, and reactants below the line.
  • Each species' concentration is raised to the power of its coefficient in the balanced equation,
  • K_c = [C]c[D]d / [A]a[B]b. (C and D are products, A and B are reactants)

Industrial Applications

  • Ammonia Production (Haber Process): High pressure and low temperature favor ammonia production.
  • Sulfuric Acid Production (Contact Process): Optimized temperature (450°C) and pressure to maximize sulfur trioxide production.

Exam Questions

  • Equilibrium Constant Expression: The expression defines the relationship of the equilibrium constant (e.g., Kp) with the concentrations of products and reactants at a given temperature.
  • Equilibrium Calculation: Equilibrium calculations (e.g., finding equilibrium concentrations or moles of reactants and products) involve using the equilibrium constant expression to find unknown concentrations.

Le Chatelier's Principle – Additional Points

  • Effect of Temperature: Temperature changes affect the value of Kc.
  • Catalysts: Catalysts increase the rate of reaction but do not change the position of equilibrium.
  • Equilibrium Position: The equilibrium position represents the ratio of product to reactant concentrations at equilibrium.
  • Dynamic nature of Equilibrium: A reversible chemical reaction in which the rate of the forward reaction is equal to the rate of the backward reaction.

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Chemical Equilibrium PDF

Description

This quiz covers the concepts of chemical equilibrium, including its definitions, reversible reactions, and the dynamic state of reactions. Additionally, it explores Le Chatelier's Principle, illustrating how changes in concentration, pressure, and temperature affect equilibrium. Test your understanding of these fundamental chemistry principles.

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