Reaction Rate Lesson

Collision Theory and Reaction Rate

Lesson 1 -Collision Theory

Lesson 2 -Factors Affecting the Rate of Chemical Reactions

Learning Competencies

• define collision theory and describe how it affects the chemical reaction; and 

• explain the different factors affecting the rate of reaction.

What I know?

15-item Pretest

Multiple Choice

A chemical change that occurs when two or more substances combine to form a new substance.

• Activation Energy

• Chemical Kinetics

• Chemical Reaction

• Product

Multiple Choice

The measure of the change in the concentration of the reactants or products.

• Activation Energy

• Activation Rate

• Chemical Reaction

• Concentration

Multiple Choice

The substance or particles that enter into and is altered in the course of a chemical reaction.

• Catalyst

• Enzyme

• Product

• Reactant

Multiple Choice

The number of particles present in a given volume of solution.

• Catalyst

• Concentration

• Product

• Temperature

Multiple Choice

The measure of how fast or slow a reaction happens.

• Activation Energy

• Collision theory

• Particle Size

• Rate of Reaction

Multiple Choice

Condition that needs to be met for a chemical reaction to occur.

• Substance must be homogeneous.

• Temperature should be kept constant.

• Particles should maintain a certain distance to each other.

• Particles in the substance must collide and have enough energy.

Multiple Choice

The factor that would NOT affect the rate of chemical reaction.

• Concentration

• Humidity

• Particle Size

• Temperature

Multiple Choice

The factor that will slow down the rate of chemical reaction.

• Manual stirring of the substance.

• Placing substance in a hot water

• Placing products in iced water.

• Placing reactants in ice bath.

Multiple Choice

The factor that does NOT show evidence of chemical reaction.

• Absorption of heat

• Change of color

• Change of size

• Liberation of heat

Multiple Choice

The measure of the hotness or coldness of a substance.

• Energy

• Humidity

• Temperature

• Thermometer

Multiple Choice

The substance formed as a result of a chemical reaction.

• Product

• Reactant

• Resistance

• Substrate

Multiple Choice

The measure of how much exposed area a solid object has, expressed in square units.

• Volume

• Surface

• Surface Area

• Concentration

Multiple Choice

The substance that is dissolved in a solution.

• Solid

• Solute

• Solvent

• Substance

Multiple Choice

The component of a solution that is present in the greatest amount.

• Sample

• Solute

• Solvent

• Substance

Multiple Choice

A form of matter that has definite composition and distinct characteristics.

• Atoms

• Compound

• Mixture

• Substance

Why do we need to understand how chemical processes takes place, be it naturally occurring or not?

• Chemical reactions common in our daily lives.

• How our body lives and grows are results of many chemical reactions that takes place, although you may not recognize them.

Chemical or Physical Change?

Identify what kind of change occurs through a poll.

Multiple Choice

Baking a pie

• Physical Change

• Chemical Change

Multiple Choice

Burning a paper

• Physical Change

• Chemical Change

Multiple Choice

Dissolving coffee in hot water

• Physical Change

• Chemical Change

Poll

Dissolving sugar in water

• Physical Change

• Chemical Change

Poll

Mixing paint to make a new color

• Physical Change

• Chemical Change

What's New?

Picture Analysis:  List down ideas you think of based on the given picture.

What's New?

Picture Analysis: Complete the sentence about reaction based on the given illustration.

A reaction.....

What is it?

Collision Theory

Collision Theory

It states that reacting substances must come into contact (collide) with enough activation energy, and in the correct orientation (facing the correct way), so that their electron shells can rearrange to form the products of the reaction.

There are two factors that determine whether a reaction will occur between two particles that are colliding: 

• Substances or particles of reactants must physically collide with enough energy

• Substance or particles must come into contact or collide in the correct orientation (facing the correct way). 

Try to analyze the illustrations given:

Figure 1: Collision between Nitrogen Gas (N₂) and Oxygen Gas (O₂)

Collision of N₂ and O₂

•  two atoms of Nitrogen react with two atoms of Oxygen to yield two molecules of Nitrogen Oxide. 

• The shared atoms form a bond by completing the valence shells of both atoms. 

Collision orientation of N₂ and O₂

As shown in figure 2, a chemical reaction does not take place if the collision between molecules does not have sufficient energy to break the bonds in the reactants and if the molecules are not properly aligned. 

As shown in figures 3 and 4, no reaction can take place between two particles if they are far apart. To form new bonds, atoms must come in contact with each other and have correct relative orientations so that the correct bonds are broken, atoms transfer to the correct positions (see also Figure 1). 

What is a Chemical Reaction?

• When two particles collide, sometimes a chemical reaction can occur, which means the bonds between two or more particles are broken and reformed, creating one or more new substances.

• The substances or particles that enter and is changed in the chemical reaction are called reactants and the substances that are formed are called products.

Chemical reaction of photosynthesis

How does it occur?

Which represent the reactants and products in the chemical reaction?

• The reactants (left part of the equation) are carbon dioxide, water, and light

• The products (right side of the equation) are sugar and oxygen

Several things must happen for a chemical reaction to occur:

• The particles must come into contact with one another or collide.

• When the particles collide, the particles must be aligned correctly so that the right parts of the atoms or molecules are exposed. If they are not oriented correctly, no chemical reaction will take place. 

• The particles must collide with enough energy to break their chemical bonds. The amount of energy that must be available for a reaction to occur is often referred to as the ACTIVATION ENERGY. It is the measure of the change in the concentration of the reactants or products. 

Reaction rate of a chemical reaction

• is a measurement of the increase in the concentration of a product or the decrease in the concentration of a reactant as the reaction proceeds over time

• *Keep in mind that not all reactions occur at the same speed. Some are very slow while others are fast.

• *The rate of reaction also depends on the type of molecules that are combining. If there are low concentrations of an essential element or compound, the reaction will be slower. 

Factors Affecting the Rate of Chemical Reaction

• Activation Energy

• Temperature

• Concentration

• Surface Area and Particle Size

1. Activation Energy

• The activation energy refers to the minimum energy required for a reaction to take place. 

• When a collision provides energy equal to or greater than the activation energy, product can form. On the other hand, if the particles have energy that is less than the activation energy, the collision is not effective, and they just bounce off each other unchanged.

The figure above shows a man trying to push a rock over the cliff. For the man to push the rock, he needs to have enough energy. If the man does not have enough energy, the rock will not move down the cliff. This energy needed for the man to push the rock over the cliff represents the activation energy. Can you think of another example to show how activation energy works?

2. Temperature

• Temperature refers to how hot or cold a certain substance is. Usually, a rise in temperature of 10 0C doubles the reaction rate. 

• The rate of a chemical reaction increases with increasing temperature. T

• As the temperature increases, collision between atoms and molecules becomes faster resulting to build up of more energy.

• The increased kinetic energy will equal to or exceed the activation energy resulting to more collisions giving rise to a reaction. 

Arrange the following samples according to the rate of solubility of sugar. (1 -fastest, 3-slowest) 

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3. Concentration

• The rate of a chemical reaction is affected by the concentration of reacting substances. 

• The term concentration refers to the number of particles present in a given volume of solution. 

• Concentration may also mean a measure of how much of of the solute (something to be dissolved) is dissolved in a solvent (dissolving medium) to form a homogeneous mixture. 

Concentration

• So, a higher concentration means there is more of the solute in the solution. 

• If the concentration of the reactant is increased, the rate of reaction also increases.

• When the number of particles of the reactant is increased, there is a great chance for particles to collide.

Now, let’s try to analyze the picture

• Based on the Kinetic Molecular Theory (KMT) and properties of matter, why do you think there is less collision on the left side while there is more collision on the right side? 

• What can you conclude about the effect of concentration on the rate of chemical reaction?

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4. Surface Area and Particle Size 

• Surface area is the measure of how much exposed area a solid object has, expressed in square units. 

• In a reaction between a solid and a liquid, the more finely divided a solid is, the faster is the rate of reaction.

•  Likewise, as you powdered a solid, its surface area becomes greater, thus the particles have higher chance of colliding and faster reaction happens.

• How many reactant particles can be seen on Figure 1?

• Which do you think is the solid particle on Figure 1? 

• What have you observed to the reactant particles in Figure 2? 

• In which container will the solid particle dissolve faster and why?