Chemistry XII Unit 3 Questions: 49 Time Limit: 49 minutes Passing Score: 60% Start Quiz Chemistry XII Unit 3 Question 1 of 49 What is chemical kinetics? Study of energy changes Study of rate of reactions and factors affecting them Study of equilibrium Study of structure What is rate of reaction? Change in temperature per unit time Change in concentration of reactant or product per unit time Change in pressure Change in volume What is unit of rate of reaction? mol mol per L mol per L per second Liters per second What is average rate of reaction? Rate at specific instant Change in concentration divided by time interval Constant rate Maximum rate What is instantaneous rate of reaction? Average rate Rate at particular instant or slope of tangent at that point Initial rate Final rate For reaction R gives P, rate of disappearance of R is: Positive delta [R] by delta t Negative delta [R] by delta t Delta [R] times delta t Delta t divided by delta [R] What is rate law or rate equation? Expression relating rate to concentrations of reactants Expression for equilibrium Expression for enthalpy Expression for entropy What is general form of rate law for A plus B gives products? Rate equals k [A] Rate equals k [A] to power m [B] to power n Rate equals [A] plus [B] Rate equals [A] times [B] What is rate constant (k)? Constant at all temperatures Proportionality constant in rate law independent of concentration Equilibrium constant Always equals 1 What is order of reaction? Sum of molecularities Sum of powers of concentration terms in rate law Number of molecules Number of steps What can be the order of reaction? Only integers Zero, integers or fractions Only positive integers Only 1 or 2 What is molecularity? Sum of orders Number of reacting species in elementary step Number of products Equilibrium ratio What are possible values of molecularity? Zero or fractions Only positive integers 1, 2, 3 Negative values Any value What is zero order reaction? Rate depends on zeroth power of concentration Rate depends on first power Rate depends on second power No reaction What is integrated rate equation for zero order reaction? [R] equals minus k times t plus [R] zero ln [R] equals minus k times t 1 by [R] equals k times t [R] equals k times t What is unit of rate constant k for zero order reaction? per second mol per L per second L per mol per second dimensionless What is first order reaction? Rate proportional to first power of concentration Rate independent of concentration Rate proportional to square of concentration Rate is constant What is integrated rate equation for first order reaction? ln [R] equals minus k times t plus ln [R] zero [R] equals minus k times t 1 by [R] equals k times t [R] squared equals k times t What is unit of rate constant k for first order reaction? mol per L per second per second or s to power minus 1 L per mol per second mol per L What is half-life (t half)? Time for 100 percent completion Time for 50 percent completion or half concentration Time for 25 percent completion Time for 75 percent completion What is half-life for first order reaction? t half equals 0.693 by k t half equals [R] zero by 2k t half equals k times t t half equals 2k What is characteristic of half-life for first order reaction? Depends on initial concentration Independent of initial concentration and remains constant Increases with time Decreases with time What is half-life for zero order reaction? t half equals 0.693 by k t half equals [R] zero by 2k t half equals ln 2 by k t half equals k What is pseudo first order reaction? True first order Higher order reaction behaving as first order due to large excess of one reactant Zero order reaction Second order reaction What is example of pseudo first order reaction? Hydrolysis of ester in presence of large excess of water Decomposition of N2O5 All reactions No reactions What factors affect rate of reaction? Only temperature Concentration, temperature, catalyst, and surface area Only concentration Only pressure How does increase in concentration affect rate? Decreases rate No effect Increases rate as more collisions occur Rate becomes zero How does temperature affect rate of reaction? Decreases rate Increases rate as more molecules have energy exceeding activation energy No effect Rate becomes zero What is temperature coefficient? Ratio of rate constants at two temperatures 10K apart Ratio of concentrations Ratio of activation energies Equilibrium constant What is activation energy (Ea)? Minimum energy required for reaction to occur Maximum energy Average energy of molecules Energy of products What is threshold energy? Activation energy Minimum energy that colliding molecules must have for effective collision Energy of products Average energy What is Arrhenius equation? k equals A times e to power minus Ea by RT k equals A times Ea k equals e to power Ea by RT k equals ln A What is A in Arrhenius equation? Activation energy Pre-exponential or frequency factor Rate constant Gas constant What is R in Arrhenius equation? Rate constant Universal gas constant equal to 8.314 J per K per mol Arrhenius constant Activation energy What is logarithmic form of Arrhenius equation? ln k equals ln A minus Ea by RT ln k equals Ea by RT ln k equals A times Ea k equals ln A How is activation energy determined graphically? Plot k versus T Plot ln k versus 1 by T giving straight line with slope minus Ea by R Plot k versus 1 by T Plot ln k versus T What is catalyst? Substance that decreases rate Substance that increases rate without being consumed Reactant Product How does catalyst increase rate? Increases activation energy Provides alternative pathway with lower activation energy Increases concentration Increases temperature What is positive catalyst? Decreases rate Increases rate of reaction No effect on rate Stops reaction What is negative catalyst or inhibitor? Increases rate Decreases rate of reaction No effect Starts reaction What is collision theory? Molecules must collide with proper orientation and sufficient energy for reaction All collisions lead to reaction No collisions needed Only energy matters What is effective collision? All collisions Collisions with proper orientation and sufficient energy leading to product formation Random collisions No collisions What is rate determining step? Fastest step Slowest step in reaction mechanism that controls overall rate First step Last step What is elementary reaction? Complex reaction Single step reaction occurring exactly as written Multi-step reaction No reaction What is complex reaction? Single step Reaction occurring in multiple steps No steps Random reaction What is intermediate? Final product Species formed in one step and consumed in subsequent step Reactant Catalyst For reaction mechanism, what determines order? Fastest step Slowest or rate determining step All steps equally Random What happens to rate constant with increase in temperature? Decreases Increases exponentially as per Arrhenius equation Remains constant Becomes zero What is relation between k1 and k2 at T1 and T2? log (k2 by k1) equals Ea by 2.303R times (1 by T1 minus 1 by T2) log k2 equals log k1 k2 equals k1 log k2 minus log k1 equals Ea Previous Next Submit Quiz Want to save your progress? Create an account or log in to track your quiz scores! Register/Login