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47 Cards in this Set
- Front
- Back
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The are that is concerned with the speeds or rates of reactions is called...
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Chemical kinetics
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The physical state of reactants (s, l, g), the concentration of the reactants (the higher the faster), the temp. of the reaction (the higher the faster), and the presence of catalysts, are all...
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Factors that affect reaction rates
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T/F: On a molecular level, reaction rates depend on the frequency of collisions between molecules.
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True
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T/F: Collisions must not only occur for reactions to take place, but they must have sufficient energy and favorable orientation.
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True
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The speed of a chemical reaction (reaction rate) is...
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The change in the concentration of reactants or products per unit of time (usually M/s or molarity per second).
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Why is there a negative sign in the rate of disappearance equation (= - Δ[A]/Δt)?
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Because rates are ALWAYS positive, and the disappearance would be negative otherwise.
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T/F: It is typical for rates to decrease as a reaction proceeds, because the concentration of reactants decreases.
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True
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T/F: In general, for aA + bB --> cC + dD
rate = (-1/a)(Δ[A]/t) = (-1/b)(Δ[B]/t), etc. |
True
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An equation which shows how the rate depends on the concentrations of reactants is called a...
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Rate law
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What is the general rate law for the equation:
aA + bB --> cC + dD ? |
Rate = k[A]^m[B]^n
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Name the rate orders of both reactants and overall in the following equation:
rate = k[NH4+][NO2-] |
First order with respect to both NH4+ and NO2-, and second order overall (1 + 1 = 2)
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If a rate is second order with respect to one reactant, what does doubling the concentration of that reactant do to the rate? Tripling?
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Doubling ([2]^2 = 4) makes it 4 times as fast, and tripling ([3]^2 = 9) makes it 9 times as fast.
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T/F: In most rate laws, reaction orders are 0, 1 or 2, but sometimes they can be fractional or even negative numbers.
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True
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What do you do when keeping up with units for k?
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Solve for k with the experimental data as usual, always keeping up with units. K can be in M^-1•s^-1, just s^-1, etc.
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What type of reaction is one whose rate depends on the concentration of a single reactant raised to the first power?
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A first order overall reaction
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The form of a rate law that expresses how rate depends on concentration is called the...
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Differential rate law
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What is the integrated rate law?
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ln[At] - ln[A0] = -kt
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If using the previous equation as y = mx + b with ln[At] as "y" and so on, and if a reaction is first order, what should the graph of time vs ln[At] look like?
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A straight, negative line.
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T/F: You can use pressure as a unit of concentration for GASES because from the ideal-gas law the pressure is directly proportional to the number of moles per unit of volume.
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True
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T/F: A second order reaction is one that depends on the concentration of one reactant raised to the 2nd power or two reactant concentrations raised to the 1st power.
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True
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T/F: If plotting 1/[At] versus time yields a straight line, then the reaction is second order.
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True
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T/F: In a first order reaction, the concentration of the reactant decreases by .5 in each of a series of regularly spaced time intervals, namely t(1/2).
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True
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OKAY. Do the half-lives of first order reactions depend on concentration? Second order?
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No; yes
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The rate constant increases with...
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Increasing temperature (the constant approximately doubles with each rise of temp by 10°C)
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The greater the number of collisions per second,...
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The greater the reaction rate
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The minimum energy required to initiate a chemical reaction is called the...
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Activation energy
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T/F: The lower the activation energy, the faster the reaction.
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True
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The fraction of molecules that have an energy equal to or greater than Ea is given by the equation...
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f = e^(-Ea/RT)
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Name the Arrhenius equation.
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k = Ae^(-Ea/RT)
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What is A in the Arrhenius equation?
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The frequency factor, the number of times collision occurs with proper orientation
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*Note, relook over the activation energy equation.
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ln(k1/k2) = (Ea/R)((1/T2) - (1/T1))
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The process by which a chemical reaction occurs is the...
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Reaction mechanism
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Reactions that occur as a result of a single collision between two molecules are known as...
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Elementary reactions
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The number of molecules that participate as reactants in an elementary reaction defines that reactions...
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Molecularity (obviously uni, bi, or termolecular)
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T/F: The chemical equations for the elementary reactions in a multistep mechanism must always add to give the chemical equation of the overall process.
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True
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A molecule created during a chemical reaction in an elementary step, but that is neither a product nor a reactant, is called an...
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Intermediate
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If a reaction is an elementary reaction, then its rate law is based directly on...
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Its molecularity
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The rate law of a unimolecular elementary reaction will be...
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First order
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T/F: The overall rate of a reaction cannot exceed the rate of the slowest elementary step of its mechanism.
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True
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Because the slow elementary step limits the overall reaction rate, it is called the...
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Rate-determining step
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T/F: The rate-determining step governs the rate law for the overall reaction.
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True
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When is it "less straightforward" to determine a rate law from a rate-determining step/elementary step?
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When the slow, rate-determining step is NOT first, and thus an intermediate might be part of this elementary step.
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T/F: Whenever a fast step precedes a slow one, we can solve for the concentration of an intermediate by assuming that an equilibrium is established in the fast step.
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True
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A substance that changes the speed of a chemical reaction without undergoing a permanent chemical change itself in the process is known as a...
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Catalyst
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A catalyst that is present in the same phase as the reacting molecules is called a...
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Homogeneous catalyst
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T/F: The catalyst is there at the start of the reaction, whereas the intermediate is formed during the course of the reaction.
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True
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A catalyst lowers the overall _ _ for a chemical reaction.
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Activation energy
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