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Energy and Rates

4U Chemistry Unit 3

QuestionAnswer
enthalpy delta H or the energy change that accompanies a physical, chemical or nuclear change
average rxn rate can be determined by the slope of the secant of a [ ]/time graph
instantaneous rxn rate can be determined by the slope of the tangent of a [ ]/time graph; generally decreases owing to fewer collisions
Collision theory reacting particles must collide EFFECTIVELY (and in the right orientation) in order for a reaction to occur. The likelihood of collisions is affected by temperature, concentration, surface area and type of reactant
rate law exponents show whether a reactant is 1st, 2nd or 3rd order.
half life of a reaction time needed for the reactant mass or concentration to decrease by half
exothermic thermochemical equation a balanced equation that shows a separate energy term in negative kJ/mol
endothermic thermochemical equation with embedded heat term a balanced equation that shows energy in kJ on the reactant side of the equation
specific heat capacity is high for water, which is why it takes so long for water to heat up or cool down
Hess's Law of heat summation algebraically adding up intermediate reactions (and their associated enthalpies) to obtain a net reaction
Qrxn is equal to the heat release (or gained) by the surroundings
Hf is the heat absorbed or released in the formation of a compound
temperature is the measure of average kinetic energy of particles
renewable energy source of energy that can be regenerated, not depleted over time (eg wind, solar and hydro)
m = 0 means that the rate of the reaction does not depend on the concentration of that reactant
reaction mechanism series of steps that make up an overall reaction; each step called an elementary reaction; molecules produced and consumed along the way are rnx intermediates
Rate-Determining Step one of the elementary reactions in the series is much slower, hence it determines the overall rate; rate law equation for rate-determining step should match the rate law for overall equation (since the slowest set affects the overall rate)
activated complex compound found at the transition stage of a reaction; is neither reactant nor product but could become either
Catalysts inorganic or biological compounds that increase the rate of reaction without being consumed because they provide an alternate rxn mechanism
Created by: jcepella