Collision-Theory. physical science module grade 11
- 2. Chemical reactions have been a part of this world ever since everything began. From Big bang to the present day, everything happening around us has something to do with chemical reactions and chemical processes.
- 3. Chemical reactions are common in our daily lives: from cooking, eating, and cleaning to the different chemical processes like respiration, corrosion, and fermentation.
- 4. How our body lives and grows are result of many chemical reactions that take place, although you may not recognize them. This is the reason we need to understand how chemical processes take place, be they naturally occurring or not.
- 5. THE COLLISIONTHEORY All substances are comprised of millions of tiny particles in constant motion. These particles are colliding with each other constantly in any substance. All collisions between particles do not result in a reaction.
- 6. THERE ARE TWO FACTORS THAT DETERMINE WHETHER A REACTION WILL OCCUR BETWEEN TWO PARTICLES THAT ARE COLLIDING: 1. Substances or particles of reactants must physically collide with enough energy 2. Substance or particles must come into contact or collide in the correct orientation (facing the correct way).
- 7. The collision theory 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.
- 8. Therefore, any factor which changes the frequency or energy of the collisions will change the rate of the reaction.
- 9. TRY TO ANALYZE THE ILLUSTRATIONS GIVEN BELOW:
- 10. 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.
- 12. 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.
- 13. 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 are changed in the chemical reaction are called reactants and the substances that are formed are called products.
- 14. LET US LOOK AT THE CHEMICAL REACTION IN PHOTOSYNTHESIS:
- 15. The reactants (left part of the equation) are carbon dioxide, water, and light while the products (right side of the equation) are sugar and oxygen. But for a chemical reaction to occur, several things must happen:
- 16. •1. The particles must come into contact with one another or collide.
- 17. • 2. 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.
- 18. •3. 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.
- 19. The 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.
- 20. The rate of reaction also depends on the type of molecules that are combined. If there are low concentrations of an essential element or compound, the reaction will be slower.
- 21. FACTORS AFFECTING THE RATE OF REACTION • 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, a 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.
- 23. 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.
- 24. • 2. Temperature • Temperature refers to how hot or cold a certain substance is. Usually, a rise in temperature of 10 0 C doubles the reaction rate. The rate of a chemical reaction increases with increasing temperature. As the temperature increases, a collision between atoms and molecules becomes faster resulting in the build-up of more energy. The increased kinetic energy will equal to or exceed the activation energy resulting in more collisions giving rise to a reaction.
- 25. • 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. 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.
- 26. • 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 powder a solid, its surface area becomes greater, thus the particles have a higher chance of colliding, and a faster reaction happens.