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Gen Chem (9)
| Question | Answer |
|---|---|
| Isobaric | An isobaric process is a type of thermodynamic process in which pressure remains constant. |
| Isochoric | An isochoric process is a type of thermodynamic process that occurs at constant volume. |
| Adiabatic | An adiabatic process is a type of thermodynamic process in which there is no heat exchange between the system and its surroundings. |
| Isothermal | An isothermal process is a type of thermodynamic process in which temperature remains constant. |
| Endothermic | An endothermic process is a type of thermodynamic process in which the system absorbs heat from their surroundings, causing a decrease in temperature. |
| What is the difference between kinetics and thermodynamics? | Thermodynamics describes whether a reaction is spontaneous; kinetics describes how fast a reaction occurs, independent of spontaneity. |
| What is the general rate expression for the reaction aA + bB → cC + dD? | Rate = −(1/a)Δ[A]/Δt = −(1/b)Δ[B]/Δt = (1/c)Δ[C]/Δt = (1/d)Δ[D]/Δt |
| Why are negative signs used for reactants in rate expressions? | Reactant concentrations decrease over time, making Δ[A]/Δt negative. The negative sign corrects this to give a positive rate. |
| What is the general form of a rate law? | Rate = k[A]ᵐ[B]ⁿ, where k is the rate constant, m and n are reaction orders determined experimentally, and only reactants are included. |
| What is the overall reaction order? | The sum of all individual reactant orders (m + n). |
| What are the three factors that affect the rate constant (k) and reaction rate? | Temperature (↑T → ↑k and ↑rate), activation energy (↓Eₐ → ↑k and ↑rate), and reactant concentration (↑[reactants] → no effect on k, but ↑rate — except in zero-order reactions). |
| What is the rate law, concentration vs. time graph, and k units for a zero-order reaction? | Rate = k [A] vs. time is linear with slope −k k units are M·s⁻¹. |
| What is the rate law, concentration vs. time graph, and k units for a first-order reaction? | Rate = k[A] ln[A] vs. time is linear with slope −k k units are s⁻¹. |
| What is the rate law, concentration vs. time graph, and k units for a second-order reaction? | Rate = k[A]² 1/[A] vs. time is linear with slope +k k units are M⁻¹·s⁻¹. |
| How do you determine reaction order from experimental data? | Hold one reactant constant between two trials, divide the rate ratio by the concentration ratio raised to a power x, and solve: (concentration ratio)ˣ = rate ratio. |
| What are the three integrated rate laws? | Zero-order: [A]t = −kt + [A]₀ First-order: ln[A]t = −kt + ln[A]₀ Second-order: 1/[A]t = kt + 1/[A]₀ |
| What is the rate determining step (RDS)? | The slowest elementary step in a reaction mechanism; it determines the overall rate law. The RDS has the highest activation energy. |
| How do you write the rate law from a reaction mechanism? | Use only the reactants and their coefficients from the RDS. The coefficients become the reaction orders (exponents). |
| What is a reaction intermediate? | A species produced in one elementary step and consumed in a later step; it does not appear in the overall reaction equation. |
| What is a catalyst and how does it differ from an intermediate? | A catalyst lowers Eₐ by providing an alternative pathway and is regenerated at the end of the reaction. An intermediate is produced mid-reaction and consumed before the reaction is complete. |
| How do you identify a catalyst vs. intermediate in a reaction mechanism? | A catalyst appears as a reactant first, then reappears as a product. An intermediate appears as a product first, then is consumed as a reactant. |
| What are the three conditions of collision theory for a reaction to occur? | Molecules must collide; they must collide with the proper orientation; they must have sufficient energy to overcome the activation energy barrier. |
| Is activation energy (Eₐ) affected by temperature? | No. Eₐ is independent of temperature. Only a catalyst can change Eₐ. Temperature helps reactants overcome Eₐ but does not change its value. |
| What is a half-life? | The time required for half the reactant to be converted to products. |
| What are the three half-life equations and how does each relate to concentration? | Zero-order: t½ = [A]₀/2k (half-life decreases as concentration decreases) First-order: t½ = 0.693/k (half-life is independent of concentration) Second-order: t½ = 1/k[A]₀ (half-life increases as concentration decreases) |
| Why are radioactive decay reactions significant in kinetics? | They follow first-order kinetics, meaning their half-life is constant and independent of the amount of reactant remaining. |
Created by:
smurtab