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# MCAT Gen. Chem Ch. 5

Term | Definition |
---|---|

Gibbs Free Energy (Delta G) | Determines whether or not a reaction is spontaneous |

Chemical Mechanisms | Propose a series of steps that make up the overall reaction |

Intermediates | Molecules that exist within the course of a reaction, but are neither reactants nor products overall |

Rate-determining Step | Limits the max. rate at which the reaction can proceed. |

Collision Theory | States that a reaction rate is proportional to the number of effective collisions between reacting molecules |

For A Collision To Be Effective, Molecules Must Be: | In the proper orientation and have sufficient kinetic energy to exceed the activation energy |

Arrhenius Equation | Mathematical way of representing collision theory |

Transition State Theory | States that molecules form a transition state or activated complex during a reaction in which old bonds are partially dissociated and the new bonds are partially formed |

Transition State | Highest point on a free energy reaction diagram |

Increasing The Conc. Of Reactants Will: | Increase reaction rate (except for zero-order reactions) because there are more effective collisions per time |

Increasing The Temperature Will: | Increase reaction rate because the particles' kinetic energy is increased. |

Changing The Medium can: | Increase or decrease reaction rate, depending on two the reactants interact with the medium |

Adding A Catalyst: | Increases reaction rate because it lower the activation energy. |

Homogeneous Catalysts | Are in the same phase as the reactants |

Heterogeneous catalysts | Are in a different phase as the reactants. |

Rate Orders Usually Do Not: | Match the stoichiometric coefficients |

Rate Order Of A Reaction | Sum of all the individual rate orders in the rate law |

Zero-order Reactions | Have a constant rate that does not depend on the concentration of each reaction |

Rate Of A Zero-Order Reaction can Only Be Affected By: | Changing the temperature or adding a catalyst |

Conc. vs Time Graph Of A Zero-Order Reaction Is A: | Straight line. The slope of the line is -k. |

First-order reactions | Have a nonconstant rate that depends on the conc. of reactant. |

Conc. vs Time Graph Of A First-order Reaction Is: | Nonlinear. The slope of a ln[A] vs time plot is -k for a first order reaction. |

Second-order Reactions | Have a nonconstant rate that depends on the concentration of reactant. |

Conc. vs Time Graph Of A Second Order Reaction Is A: | Nonlinear curve. Slope of a 1/[A] vs time plot is k for a second-order reaction. |

Broken-order Reactions | Reactions with noninteger orders. |

Mixed-order Reactions | Reactions that have a rate order that changes over time. |

Eq. 5.1: Collision Theory | Rate = Z x f. Z = total number of collisions per second. f = fraction of collisions that are effective. |

Eq. 5.2: Arrhenius Equation: | k = Ae ^ - Ea / RT. k = rate constant of reaction. A = frequency factor. Ea = activation energy of reaction R = idea gas constant, 8.314 J/k*mol. T = temperature in Kelvin. |

Eq. 5.3: Definition Of Rate | Rate = - Delta[A] / a*Delta t = - Delta[B] / b * Delta t = Delta[C] / c * Delta t = DeltaD] / d * Delta t. For the general reaction aA + bB --> cC + dD |

Eq. 5.4: Rate Law | Rate = k[A]^x[B]^y. k = reaction rate coefficient / constant. x and y = orders of the reaction. |

Eq. 5.5: Radioactive Decay | [A]t = [A]0 * e^-kt. [A]t = conc of A at time t. [A]0 = initial conc of A. k = rate constant. t = time. |