Chemical Equilibrium Practice Flashcards

Vocabulary-style flashcards based on chemical equilibrium, Le Chatelier’s principle, and industrial chemical processes.

Dynamic Equilibrium

A state that occurs in reversible reactions when the forward and backward reactions are occurring at equal rates, resulting in constant concentrations of reactants and products.

Position of Equilibrium

An expression used to describe the composition of the equilibrium mixture; it is said to favour the reactants (shift towards the left) or products (shift towards the right).

Le Chatelier’s Principle

A principle stating that if an external condition is changed the equilibrium will shift to oppose the change.

Effect of Temperature Increase

The equilibrium will shift to oppose this by moving in the endothermic direction to reduce the temperature by absorbing heat.

Effect of Temperature Decrease

The equilibrium will shift to oppose this by moving in the exothermic direction to increase the temperature by giving out heat.

Compromise Temperature

A temperature used in industrial processes (like the Haber process) that balances the need for a reasonable yield (favored by low temperatures in exothermic reactions) with an acceptable rate of reaction (favored by high temperatures).

Effect of Pressure Increase

The equilibrium will shift towards the side with fewer moles of gas to oppose the change and reduce the pressure.

Effect of Pressure Decrease

The equilibrium will shift towards the side with more moles of gas to oppose the change and increase the pressure.

Effect of Concentration Increase

Increasing the concentration of a substance (e.g., $OH^-$ ions) causes the equilibrium to shift to oppose this and move in the direction that removes those ions.

Effect of Catalysts on Equilibrium

A catalyst has no effect on the position of equilibrium because it speeds up the rates of the forward and backward reactions by the same amount, though it increases the rate at which equilibrium is reached.

Haber Process Conditions

The industrial production of ammonia where temperature is $450^{\circ}C$, pressure is $200 - 1000\,atm$, and the catalyst used is iron.

Contact Process Stage 2

The reaction $SO_2 (g) + \frac{1}{2} O_2 (g) \rightleftharpoons SO_3 (g)$ ($\Delta H = -98\,kJ\,mol^{-1}$) using a temperature of $450^{\circ}C$, pressure of $1\text{ to }2\,atm$, and a $V_2O_5$ catalyst.

Hydration of Ethene Conditions

The process $CH_2=CH_2 (g) + H_2O (g) \rightleftharpoons CH_3CH_2OH (l)$ uses a temperature of $300^{\circ}C$, pressure of $70\,atm$, and a concentrated $H_3PO_4$ catalyst.

Production of Methanol from CO

The reaction $CO (g) + 2H_2 (g) \rightleftharpoons CH_3OH (g)$ ($\Delta H = -ve$) uses a temperature of $400^{\circ}C$, pressure of $50\,atm$, and chromium and zinc oxide catalysts.

Industrial Pressure Trade-offs

While high pressure can increase yield and rate, it leads to high electrical energy costs for pumping gases and expensive equipment to safely contain the pressure.

Equilibrium Constant ($K_c$)

An expression representing the ratio of products to reactants at equilibrium: $K_c = \frac{[C]^p [D]^q}{[A]^m [B]^n}$ where square brackets indicate equilibrium concentrations in $mol\,dm^{-3}$.

Effect of Temperature on $K_c$

$K_c$ only changes with temperature; it is not altered by changes in pressure, concentration, or the addition of a catalyst.

Heterogeneous $K_c$ Expressions

In these expressions, liquid and solid concentrations are considered constant and are therefore not included.