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chemistry > kinetics > Flashcards

kinetics Flashcards

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1
Q

state when reactions occur?

A

when collisions take place between particles with sufficient energy to break the bonds in the correct orientation

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2
Q

what 2 factors does the rate depend on?

A

frequency of collisions and success of collisions

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3
Q

in order to increase the rate of reaction we need to increase the number of ……?

A

succesful collisions

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4
Q

what are 4 things we can add/change to influence the rate?

A

add catalyst, change temp, pressure, surface area

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5
Q

how can an increase in concentration increase pressure ?

A

more particles present in a given volume so increase in pressure

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6
Q

define activation energy

A

minimum energy needed to start a reaction

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7
Q

define rate of reaction

A

speed at which a chemical reaction takes place

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8
Q

state rate of reaction units

A

mol dm^-3 s^-1

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9
Q

state what an ineffective collision is

A

when particles collide in wrong orientation or not enough energy to bounce off each other without causing a reaction

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10
Q

state the meaning of collision frequency ?

A

number of collisions per unit time

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11
Q

why does a Maxwell boltzsman start at the origin ?

A

no particles have zero energy

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12
Q

what and where is the most probable energy on a Maxwell boltzsman and why?

A

the energy that most particles have, at the peak on the curve because that is where most particle are

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13
Q

what does the area under the curve of a Maxwell boltzsman represent ?

A

number of particles

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14
Q

label the y and x axis on a Maxwell boltzsman graph

A

y- number of particles / molecules
x- energy

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15
Q

where would the mean energy be on a Maxwell boltzsman graph ?

A

to the right of the peak because there are some particle that have higher energy that the MPE which brings the average up

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16
Q

what happens to a Maxwell boltzsman distribution when temperature is lowered ?

A

area under curve stays same
peak moves left (lower energy )
peaks gets higher and more particles having less energy

17
Q

what happens to a Maxwell boltzsman distribution when temperature is increased ?

A

peak gets higher and lower

18
Q

in an exothermic reaction do particles or reactants have higher energy?

A

reactants

19
Q

in an endothermic reaction do particles or reactants have higher energy?

A

products

20
Q

what does an increase In reaction rate mean for the Ea?

A

greater proportion of molecules have energy equal or higher than Ea

21
Q

how does a catalyst increase rate if reaction ?

A

provides an alternate pathway for a reaction, one which has lower Ea. it is chemically unchanged

22
Q

what effect does increasing concentration have on the rate of reaction ?

A

more particles in a given volume in the higher concentration solution therefore increasing the number of successful collisions and increasing the rate of reaction

23
Q

what effect does increasing temperature have on the rate of reaction ?

A

particles have higher kinetic energy so more frequent collisions and increases rate of reaction

24
Q

what effect does increasing pressure have on the rate of reaction ?

A

particles closer and collide more often (more frequent collisions) so a higher chance of a reaction starting

25
Q

what is a homogenous catalyst?

A

catalyst in same phase as the reactants

26
Q

what is a heterogenous catalyst ?

A

catalyst in different phase as the reactants

27
Q

explain the effect that a catalyst has on a Maxwell-boltzman ?

A

shifts Ea to left because more particles to the right of the Ea

28
Q

why do most reactions not take place?

A

don’t have sufficient energy or in the wrong orientation

29
Q

why would a small temperature increase lead to a big increase in rate?

A

a higher percentage of collisions will result in a reaction

30
Q

what does an increase in temperature do to the Ea ?

A

more molecules will have enough energy to react (higher than Ea)

31
Q

state the effect a catalyst has on enthalpy change

A

it won’t effect it

chemistry (9 decks)

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