CHEM 112 Exam 2 Questions With Multiple Choices And Correct Answers

What is reaction rate a ratio of? - correct answers concentration of reactant or product per unit time (Δ[A]/Δt) What does a rate law do? - correct answers shows how rate depends on concentrations of reactants (ex. rate = k[A]²[B]) What do exponents in a rate law represent? How can they be determined? - correct answers reaction order, which can only be determined experimentally (not from balanced equation) Why do concentrations of products not appear in the rate law? - correct answers reaction is studied under conditions where reverse reaction does not contribute to the overall rate What is the difference between a differential and integrated rate law? - correct answers differential: how rate depends on concentrations integrated: how concentrations depend on time How can you calculate the overall reaction order? - correct answers sum of exponents in reaction rate equation What are the normal rate law and integrated rate law for a first order reaction? - correct answers normal: rate = k[A] integrated: ln[A]t = -kt + ln[A]₀ How do you calculate the half life of a first order reaction? - correct answers half life₁ = 0.693/k What does the half life of a first order reaction not depend on? - correct answers concentration of reactants What are the normal rate law and integrated rate law for a second order reaction? - correct answers normal: rate = k[A]² integrated: 1/[A]t = kt + 1/[A]₀ How do you calculate the half life of a second order reaction? - correct answers half life₂ = 0.693/k[A]₀ What are the normal rate law and integrated rate law for a second order reaction? - correct answers normal: rate = k[A]⁰ = k integrated: [A]t = -kt + [A]₀ How do you calculate the half life of a zero order reaction? - correct answers half life₀ = [A]₀/2k What are the three possible molecularities of elementary steps? - correct answers unimolecular: reaction involving one molecule (first order) bimolecular: reaction involving the collision of two species (second order) termolecular: reaction involving the collision of three species (third order) What are the two components the rate-determining step determines for the overall reaction? - correct answers rate constant and molecularity What are the three main factors in the collision model of kinetics, that molecules must collide to react? - correct answers 1. activation energy (Ea) 2. temperature 3. molecular orientations What is the Arrhenius equation in its linear form? How would you rearrange it to actually use it? - correct answers ln(k) = -Ea/R(1/T) + ln(A) ln(k₂/k₁) = Ea/R(1/T₁-1/T₂) How does a catalyst speed up a reaction? - correct answers by providing a new pathway for the reaction that has a lower activation energy What is the difference between a heterogeneous catalyst and a homogenous catalyst? - correct answers heterogeneous: gaseous reactant, solid catalyst homogeneous: catalyst same phase as reactants Does catalyst concentration change as a reaction proceeds? - correct answers no Define energy. - correct answers capacity to do work or produce heat What two components does kinetic energy depend upon? - correct answers mass and velocity Define work. - correct answers force acting over a distance What is the difference between an endothermic reaction and an exothermic reaction? - correct answers endothermic: heat flows into system, energy is absorbed from surroundings exothermic: energy flows out of system What does the variable q represent? - correct answers heat What is the first law of thermodynamics? - correct answers law of conservation of energy What sign is q for an endothermic reaction? What about for an exothermic reaction? - correct answers endothermic: +q exothermic: -q What is the equation for calculating work? - correct answers w = PΔV What is enthalpy, and what symbol denotes it? - correct answers total energy in a system, ΔH When does enthalpy equal heat, or ΔH = q? - correct answers constant pressure What is Hess' Law roughly? - correct answers change in energy is the same no matter how many elementary steps the reaction is broken into What is standard enthalpy of formation? - correct answers the change in enthalpy that accompanies the formation of one mole of the compound from its elements What is the heat of formation for an element at 1 atm and 25º C? - correct answers zero What is a combustion reaction? - correct answers hydrocarbon + O₂ → CO₂ + H₂O What would the equation be for the equilibrium coefficient of this reaction: A + 2B ⇌ 3C + 4D? - correct answers K = [C]³[D]⁴/[A][B]² How do you find K (equilibrium constant) for a reverse reaction? - correct answers reciprocal What is equilibrium position? - correct answers a set of equilibrium concentrations What is the calculative relationship between K (equilibrium constant based on concentration) and Kp (equilibrium constant based on pressure)? - correct answers Kp = K(RT)^Δn What is the difference between heterogeneous equilibria and homogeneous equilibria? - correct answers homogeneous: one phase heterogeneous: multiple phases Which phases are considered and which are not when calculating equilibrium constant? - correct answers (g) and (aq) considered, (s) and (l) not What does the size (, 0) of K (equilibrium constant) say about where the equilibrium lies and what it favors? - correct answers K 0: product-favored, right K 0: reactant-favored, left What is Q? - correct answers the reaction quotient What is the law of mass action involved with? - correct answers shifting of reaction to reach equilibrium again Where does the system shift depending on the relationship between K and Q? - correct answers Q = K: equilibrium Q K: shift left Q K: shift right What principle describes the shifting of a system to r