Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.

Normal Size Small Size show me how

Normal Size Small Size show me how

# Chem107:

### chapter 15

Question | Answer |
---|---|

Chemical kinetics | study of the rates of chemical reactions |

chemical kinetics | studies how to determine a reaction rate experimentally and how factors such as temp. and concentration of reactants influence reaction rates. also studies the pathway taken by atoms/molecules as the reaction proceeds |

Rate of reaction | change in concentration/change in time |

rate of reaction-given this reaction: N2O5->2NO2+1/2O2 (rate of rxn can be written several ways based on decrease of N2O5 w time/the increase in NO2 w time or the increase in 02 w time | -<|[N2O5]/<|t -- for reactant bc concentration will be decreasing +1/2(<|[NO2]/<|t] +2<|[O2]/<|t -(t) for products bc concentration will be increasing |

the rate of decomposition of N2O5 is | to 1/2 the rate of formation of NO2 and twice the rate of formation. rate expressions |

Factors that affect the rate of a rxn: | reactant concentration temp presence of catalyst surface area (if a solid is reacting) |

reactant concentration | As RC^ the rate of the rxn ^ in most situations |

Temp | when temp ^ reactions usually speed up |

presence of a catalyst | a catalyst is a substance that increases the rate of rxn w being consumed in the overall (net) rxn. a catalyst is usually written over the arrow in an equation |

surface area | bc reactions occur at the surface of a solid, rxn rates ^ w an ^ in surface area |

effects of concentration on reaction rates | by evaluating how the rxn rate is affected when the concentrations of the reactants are varied, the effect of concentration can be determined (temp must be kept constant) |

ex. A+B->C rate of disappearance of a: .30m/l*min | if we double the [] of A and calculate the rate of disappearance & found it be .60m/l*min, we could say that the rate of rxn is directly proportional to the [] of reactant A |

ex. A+B->C rate of disappearance of a: .30m/l*min | if we halved the [] of A and the rate changed to .15m/l*min is the rxn rate still directly proportional to [] of reactant A? |

some reaction rates | can be dependent of [] or the rxn rate may be dependent on the reactant [] raised to some power |

if rxn contains more than 1 reactants | the rxn rate may depend on the concentrations of each of them or only one of them *note:rxn rate can also depend on catalyst concen or even product [] |

relationship bt reactant [] and rxn rate | expressed by an equation called a rate equation or rate law |

in rate law | there is proportionally constant bt rate & concentration called rate constant (K) the rate constant is specific w each temp and varies with temp |

reaction orders: | rate=K[A][B]2 K[A]/rate-directly proportional rate/[B]2-exponentially proportional 2x rate=k[2A][B]2 4x rate=k[4A][2b]2 (powers to which concentrations are raised are called reaction orders) |

reaction orders: | rxn rates must be compared to compare rates/make ratio (rate of doubled conc/rate of original=rate change factor) now use following equation to solve for rxn order for the specific reactant X(exponent)=log of rate change factor/log of conc change facto |

reaction orders: a rxn is | the exponent to which [] of substance is raised in rate law |

concentration time equations | we sue concentrations time equations to determine how long it would take for a pre determined amount of reactant remaining after a certain amount of time |

for first reorder reactions | c.t.equation is ln[R]t/[R]o=-kt or log[R]t/[R]o=-kt/2.303 |

for second order reactions | c.t.equation= 1/[R]t - 1/[R]o=Rt |

Half life of a rxn | as a reaction procceeds, the concentration of a reactant decreases bc it is being consumed |

half life of a rxn | the half life-the slower the rxn/h.l. is used mostly w 1st order reactions. |

half life (t1/2) can be calculated using this equation: | t1/2=.693 for 1st order reactions. half life is independent of concentrations. |

collision theory | for this rxn: NO+Cl->NOCl+Cl -a 10 degrees rise in temp causes the rate of rxn to triple. this shows tha rate of rxn is very dependent on temp. |

collision theory | states that for rxn to occur, reactant molecules or particles must collide with an energy greater than some minimum value & must collide w proper orientation |

activation energy (Ea) | the minimum energy of collision required for 2 molecules or particles to react is called |

in collision theory, | the rate constant (k) is considered a product of 3 factors k=zfp |

k=zfp | z=collision frequency f=fraction of collisions w energy greater than activation energy p=fraction of collisions that are properly oriented |

concentration affects ___ more | Z |

temperature affects ____ more | f |

catalysts lower ____ so rxns can go faster | Ea |

we cannot control _____ | p |

transition state theory | explains a rxn in terms of an activated complex. a.c. is a transition state. unstable grouping of atoms |

Reaction with a large ____ run _____ | Ea/slow |

Reactions with a small ____ run ____ | Ea/fast |

the effects of catalysts on reaction rate | catalysts used to speed up a rxn/not consumed in rxn function-provide diff pathway to Ea for rxn |

catalysts allow rxn | to proceed at higher (take less time) and at a lower (lower temp, lower energy costs) |

enzymes | catalysts-biological cell contains thousands of diff enzymes |

reaction mechanisms | elementary reactions give us reaction mechanism |

sum of elementary rxns give us | overall net reactions |

molecularity | -how elementary rxns are classified -number of molecules or particles on the reactant side of elementary rxn |

rate law for an elementary can be predicted by looking at rxn | rate law is prop to product of conc of each reactant |

remember | this predicted rate law must be compared to experimental rate law/may or may not be true |

elementary reactions/reaction order | 1st order-unimolecular 2nd order-bimolecular |

Created by:
dixxfranks