Kinetics and Reaction Rates Study Guide, Exams of Chemistry

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PORTAGE CHEM 104 MODULE 1 STUDY GUIDE Latest Questions with Answers Kinetics - answers the study of rates of reactions and how they are influenced by certain factors Influences Reactions Rates - answers Concentration, temperature, catalysts, surface area Temperature/Reaction Rate - answers Increase, higher temperature provides higher kinetic energy Catalyst/Reaction Rate - answers Increase, without being consumed Surface Area/Reaction Rate - answers Increase, increased surface area of particles increases reaction rate because solids only react at their surfaces (grinding solid into fine powder) Concentration/Reaction Rate - answers Increase, provides more reacting particles to undergo reaction Reaction Rate - answers Increase in molar concentration of product per unit of time or the decrease in molar concentration per unit of time Reaction Rate Units - answers moles per liter per second (mol/L*s) Reaction Rate Equation - answers Change in concentration/change in time (products=positive, reactants=add negative sign) Average Rate - answers Determined by using initial and final concentrations and initial and final times so that the result measures the rate over the entire reaction Instantaneous Rate - answers the change in concentration of reactants (or products) divided by a very short period of time Instantaneous Rate Decreases... - answers Decreases, as reaction proceeds, concentration of reactant becomes smaller due to consumption of reactants as reaction takes place Early Instantaneous Rate - answers the change in concentration of reactants (or products) divided by a very short period of time near the beginning of the reaction Half-Life Definition - answers the time required for one-half of a reactant to undergo the reaction Given 50% remaining - answers ln (50) - ln (100) = k t 1/2 Given half-life, use to find K, find T - answers 0.693 = k t 1/2 Catalyst - answers Substance that increases the rate of a chemical reaction without itself being consumed; combines with reactants to form new intermediate that is able to react more readily to form the product and regenerates the catalyst as the product is formed Effect of Solvent - answers Reactions in solution allow the particles to come in contact with one another more freely causing a higher rate of reaction Effect of Stirring - answers stirring a heterogeneous mixture increases the amount of contact between particles causing a higher rate of reaction Effect of Concentration - answers a higher concentration causes this greater number of particles to collide more often which results in a higher rate of reaction Effect of Temperature - answers a higher temperature causes faster moving particles which collide more often and with energy greater than the activation energy causing a higher rate of reaction Collision Theory - answers Particles must collide with sufficient activation energy and proper alignment Enzymes - answers Protein catalysts present in living systems that promote reactions 3 Factors Rate Depends on (Collision Theory) - answers Depends on how often particles collide, how many of these collisions have the proper alignment, how many of these collisions have energy greater than required activation energy Transition State - answers when the reactant molecules are provided with energy equal to the activation energy, combine to form transition state, an unstable complex of atoms that can decompose to form products Relatively Large Activation Energy (E act) - answers Nonspontaneous reaction requiring input of a lot of energy to occur Positive Heat of Reaction (+Delta H) - answers Endothermic Reaction Relatively Small Activation Energy (E act) - answers Spontaneous reaction requiring no additional energy other than that provided at room temperature to occur Negative Heat of Reaction (-Delta H) - answers Exothermic reaction Elementary Reactions - answers Individual reactions that constitute steps of a reaction mechanism Molecularity - answers the number of reactant particles in an elementary reaction Bimolecular - answers two reactant molecules Unimolecular - answers one reactant molecule Termolecular - answers three reactant molecules (rare) Rate-Determining Step - answers the slowest step in a reaction mechanism Overall - answers the _____ reaction rate is equal to the rate of the slowest step Equilibrium Reactions - answers do not go to completion, significant reactant is wasted Method 1 Shifting Equilibrium Reactions - answers changing the concentrations by adding or removing reactants or products Method 2 of Shifting Equilibrium Reactions - answers Changing the partial pressure of gaseous reactants or products by changing the volume Method 3 of Shifting Equilibrium Reactions - answers Changing the temperature Reaction Thrown Out of Equilibrium - answers will attempt to re- establish equilibrium Le Hotelier’s Principle - answers when a system at equilibrium is disturbed by a change of temperature, pressure or concentration, the system shifts in equilibrium composition so as to counteract the change imposed on it Increase yield of Product (concentration) - answers Remove product, add reactant Concentration (at equilibrium) Increased - answers Reaction shifts in the direction that consumes some of that added material to re-establish equilibrium Concentration (at equilibrium) Decreased - answers Reaction shifts in the direction that produces some of that removed material Increase yield of a Product (pressure) - answers Change the volume of a reaction changes the partial pressure of moles of gas, effectively changing the concentrations of those gases Pressure and Volume Relationship - answers inversely related Pressure doubled, volume ______ - answers halved Pressure (at equilibrium) Increased - answers Reaction shifts in the direction that decreases the pressure by going toward the side with the lesser moles of gas Pressure (at equilibrium) Decreased - answers Reactions shifts in the direction that increases the pressure by going toward the side with the greater moles of gas States of Matter Considered in Determining Effect of Pressure on Equilibrium Ran - answers Gases ONLY How does temperature affect Kc? - Answers Affects the NUMERICAL value of Kc Temperature Increased, Negative Delta H - answers Reaction shifts in the reverse direction to use up some of added heat (-delta H=exothermic (heat producing) forward ran) Temperature Increased, Negative Delta H Effects Kc - answers Reverse decreases concentration of products (numerator in Kc) and increases concentration of reactants (denominator in Kc) which DECREASES VALUE of Kc Temperature Increased, Positive Delta H - answers Reaction shifts in the forward direction to use up some of the added heat (+delta H=endothermic (heat absorbing) forward ran) Temperature Increased, Positive Delta H Effects Kc - answers Forward increases concentration of products (numerator Kc) and decreases concentration of reactants (denominator Kc), which INCREASES VALUE of Kc