chemistry m4 rates
TRANSCRIPT
OBJECTIVES
At the end of this presentation, you should be able to:• define rate of reaction• identify at least four factors which affect the rate of a
chemical reaction • explain how the factors cited affect the rate of
reaction• illustrate graphically how a catalyst alters the rate of
reaction• describe two ways that reaction rate can be
measured.
COLLISION THEORY
For a reaction to occur the particles (atoms, molecules) have to collide with each other.The more frequently they collide, the faster the rate of reaction.For a reaction to occur the particles must have a minimum amount of energy. This is called the ACTIVATION ENERGY.
EFFECT OF CONCENTRATION
• In a concentrated solution, there are more solute particles per unit volume. Increasing the concentration, increases the probability of a collision between the reactant particles since there are more of them in the same volume.
• Hence, the greater the concentration, the greater the frequency of collision and the faster the rate of reaction.
EFFECT OF TEMPERATURE
• As the temperature increases, the frequency of collision increases and more particles gain the activation energy necessary for the reaction to take place.
• Hence, as temperature increases, the faster the rate of reaction.
EFFECT OF SURFACE AREA
• If a solid reactant is broken down into smaller pieces the rate of reaction increases.
• The particles now have a greater surface area compared to larger pieces of the solid.
• Hence, there is more chance of a reactant particle colliding with the solid surface
• As the frequency of collision increases, the faster the rate of reaction.
EFFECT OF PRESSURE
Pressure is only considered when gases are involved. Look at the diagrams below and explain how the rate is affected when there is an increase in pressure.
EFFECT OF CATALYST
• A catalyst speeds up the rate of a chemical reaction by providing an alternate pathway of lower activation energy.
• Since the activation energy is reduced, more particles will have enough energy to result in a reaction.
EFFECT OF CATALYST
• Observe the energy profile diagram for an endothermic reaction with and without a catalyst.
• Now draw the energy profile diagram for an exothermic diagram with and without a catalyst.
MEASURING THE RATE OF A REACTION
Two common ways:• Measuring how fast the products are being
produced.• Measuring how fast the reactants are being
used up.
Measuring how fast the products are being produced.
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Measuring how fast the reactants are being used up
Visit the following link for information:• http://johnwest.edublogs.org/2009/08/18/ncea-level-2-chemistry-rates-o
f-reaction-strong-and-weak-acids/