click below
click below
Normal Size Small Size show me how
Energy and Rates
4U Chemistry Unit 3
Question | Answer |
---|---|
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 |