chem

Chemical Equations and Reactions

Writing Chemical Equations

• Chemical equations follow a convention of having reactant formulas on the left of a reaction arrow and product formulas on the right.

• The equation represents a reaction proceeding from left to right.

• Reversible Reactions: Can proceed both forward (left to right) and backward (right to left).

Equilibrium in Reversible Reactions

• At equilibrium, the rates of forward and reverse reactions are equal.

• Concentrations of reactants and products remain constant over time.

• Variability in Equilibrium:

  • Some systems favor products.

  • Others favor reactants.

  • Some have significant amounts of both.

Example: Dinitrogen Tetroxide Equilibrium

• Reaction represented as:[ N_2O_4(g) \rightleftharpoons 2NO_2(g) ]

• A special double arrow indicates the reaction is reversible.

Observing Chemical Equilibria

Changes in Concentration

• Figure 13.2 (a): Sealed tube containing colorless N2O4 darkens as it decomposes into brown NO2.

• Figure 13.2 (b): Changes in concentration of both reactants and products over time until equilibrium is reached.

Understanding Reaction Rates

• Rates can be expressed using rate laws based on stoichiometry:

  • Forward Reaction Rate:[ rate_f = k_f [N_2O_4] ]

  • Reverse Reaction Rate:[ rate_r = k_r [NO_2]^2 ]

Dynamic Nature of Chemical Equilibrium

Reaction Progress

• At time t = 0:

  • N2O4 concentration is finite; NO2 concentration is zero.

• As the reaction progresses:

  • N2O4 is consumed, its concentration decreases.

  • NO2 is produced, its concentration increases.

• Equilibrium is reached when forward and reverse reaction rates are equal.

Characteristics of Equilibrium

• Equilibrium is dynamic:

  • Reactions proceed in both directions at equal rates, sustaining constant concentrations of reactants and products.

Equilibrium Beyond Chemical Reactions

Illustrating Dynamic Equilibria

• Figure 13.3: Juggling act analogy to demonstrate dynamic equilibria.

  • Each person throws and catches at the same rate maintaining a constant number of clubs.

Reversible Physical Changes

• Examples include phase transitions, like the vapor pressure of liquids or solids.

• Bromine Phase Transition:[ Br_2(l) \rightleftharpoons Br_2(g) ]

• Forward process (vaporization) begins when liquid bromine is introduced to a sealed container.

• Reverse process (condensation) rate increases until equilibrium with vaporization is reached.

Visualizing Phase Equilibrium

Evidence of Machine Dynamics

• Figure 13.4: Photo of equilibrium mix of liquid and gaseous bromine in a sealed tube.