Reaction Kinetics Introductory lesson

Reaction Kinetics The study of the rates of reactions and the factors which affect the rates. What is a reaction rate? the rate at which a product is formed or a reactant is consumed. Always an average rate

Reaction Kinetics Rate =

How can we monitor the rate? There are four main methods to observe the rate of a reaction according to properties: 1- Colour change 2- Temperature change

How can we monitor the rate? 3- Pressure change 4- Mass change

What makes a reaction? Collision Theory  Reactions occur when molecules __________  Not all collisions result in new materials. In order for the reaction to occur, collisions must have: 1. __________________ 2. __________________

What makes a reaction? In other words, there are two main features about collisions that affect the rate of a reaction. 1. effectiveness of collision(geometry, energy) 2. frequency of collision

What makes a reaction? If proper geometry and energy is achieved, a structure called an ____________________ is formed. This structure is _______________ as it only exists long enough for molecules to ______________ themselves to form products The minimum amount of energy needed to form the activated complex is called the ________________. Ex:

Creating a Successful Collision 1. Sufficient Energy a) Energy <E a - they rebounce off each other resulting in an ineffective collision. b) Energy = E a - molecules come to a stand-still but a reaction will be possible. c) Energy > E a - molecules will lock together forming an Activated Complex while they are moving through space.

Creating a Successful Collision 2. Correct alignment If reactants are not correctly aligned then the reaction needs more energy to be completed. They have to face each other from the right angles

Correct Geometry

Correct Geometry & Energy

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Nature of reactants Reactions in which there are only slight ___________________ are usually rapid at R.T. (ionic substances in solutions tend to be fast reactions) Reactions with many covalent bonds to break are usually slow at R.T. Concentration of reactants the rate of chemical reactions usually ________ as the concentration of reactants increases assuming a homogeneous reaction for gases you can increase the concentration by Supplementary to Lesson #3 What affects the rate?

What affects the rate? Temperature increasing the temp__________ the reaction rate for two reasons  It increases the speed of the molecules  increasing the number of collisions.  It increases the number of molecules that have enough ________ to make the reactions go

What affects the rate? Pressure When the pressure of a gaseous reactant increases, more of the reactant is compressed into a given volume, in other words, concentration increases, and therefore the rate ___________ Catalysts  A substance that speeds up a chemical reaction ________ being permanently altered itself.  It provides a low energy pathway from the reactants to products by lowering the _____________ and forming a lower energy activated complex  It does this by helping orient the molecules so there are more effective collisions

What affects the rate? Surface area (& phase considerations) The greater the surface area available for the reaction, the _____________________ Increasing surface area increases the number of collisions between reacting molecules It is also important to consider the phase of the reactants: A Homogeneous reaction is a reaction in which all the reactants ______________________ two gases two substances dissolved in water A Heterogeneous reaction is a reaction in which the reactants are present in different phases. solid and a liquid liquid and a gas

What affects the rate? Another important consideration is overall phase. The following trend in reaction rates is found Fastest  Slowest Aqueous > (Gases or Liquids) > Solids

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