Chemistry Rate Laws Quiz

Study Notes

The rate of a chemical reaction depends on the concentrations of reactants and temperature.
Rate law formulation: For the reaction aA + bB ⟶ cC + dD, the rate can be expressed as Rate ∝ [A]^x [B]^y.
Introducing a constant of proportionality k transforms the expression into Rate = k [A]^x [B]^y, where:
- k is the rate constant specific to the reaction and temperature.
- Exponents x and y represent the order of the reaction with respect to A and B, respectively.
The order indicates how reaction rates change based on reactant concentrations.
Coefficients in the balanced equation do not dictate the exponents in the rate law.
Rate law parameters must be determined experimentally, often using initial rate methods.

Spectrometric techniques monitor the concentration of light-absorbing species.
Example reaction: NO(g) + O3(g) ⟶ O2(g) + NO2(g) (brown).
Measure concentration changes of NO2 to calculate reaction rates via light intensity.
Conductometric methods detect changes in solution conductivity due to shifts between ionic and nonionic states.

Specific system and surroundings temperatures: T_system = 403 K, T_surr = 305 K.
Heat exchange: q_system = -340 J, q_surr = +340 J, leading to a final temperature Tf = 300 K.
Calculated changes in entropy:
- ΔS_system = -0.84 J/K.
- ΔS_surr = +1.11 J/K.
Total change in entropy for the universe (ΔS_univ = ΔS_system + ΔS_surr) yields ΔS_univ = +0.27 J/K.

Heat of combustion for benzene determined via bomb calorimetry: 3263.9 kJ/mol at 25°C.
Reaction for benzene combustion: C6H6 + 7O2 ⟶ 6CO2 + 3H2O, with the derived reaction affording H+ and OH- ion interaction data.
Enthalpy changes for combustion and hydrogenation are computed using known enthalpy values for reactants and products:
- CO2 and H2O formation from C2H4 employs combustion enthalpy values for calculations (e.g., -393.5 kJ/mol for CO2).
The process of hydrogenation for ethylene involves calculating the changes based on the combustion of C2H4 and other related substances.

Constant volume reactions can be analyzed for energy changes, emphasizing the significance of enthalpy and behavior under both constant pressure and volume conditions.
Understanding these principles is crucial for mastering chemical thermodynamics and energetics.