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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 |
Created by:
jcepella