COLLISION THEORY AND REACTION RATES

Transcription

1 COLLISION THEORY AND REACTION RATES

2 WHAT IS COLLISION THEORY All matter is made of atoms and these atoms are in constant motion. (some particles move faster than others) Collision theory applies to gas particles. Solids & liquid particles are less likely to collide as they are moving slower.

3 NOT ALL COLLISIONS ARE EQUAL When moving particles collide, some collisions result in a chemical reaction. successful reactant collisions result in a chemical reaction and product formation (effective collisions) unsuccessful reactant collisions do not produce products, the chemical reaction does not occur (ineffective collisions) To be a successful collision, the reactant particles must have enough energy to overcome the activation energy barrier. Activation energy is the energy required to break reactant bonds, so atoms can rearrange and form products. (bond breaking absorbs energy)

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5 POTENTIAL ENERGY DIAGRAM ACTIVATION ENERGY products ACTIVATION ENERGY (E A ) The energy required for (bond breaking) reaction to occur reactants Energy barrier/threshold

6 Why are collisions so important? The more collisions, the more likely a chemical reaction will occur. Increasing collisions will increase the rate of a reaction More collisions, the faster the reaction creates products As a reaction takes place, the reactants are transferred into products

7 FACTORS THAT INFLUENCE COLLISIONS/REACTION RATES There are 5 Major Factors that effect the amount of collisions that occur and thus the reaction rate Temperature Concentration Surface Area Pressure Catalysts

8 Factor #1: Temperature Temperature: a measure of the kinetic energy of the particles in a substance Increasing the temperature = increasing the kinetic energy (move faster) The faster the particles move, the more likely there are to be successful collisions If you increase the temperature, you increase the collisions, and increase the reaction rate

9 Factor #2: Concentration Concentration: the measurement of the amount of solute that is dissolved in a given quantity of solvent; usually expressed in mol/l This is essentially increasing the number of particles in the same space (think of the PhET) If you increase the amount of particles, they are more likely to collide with each other and cause products to form If you increase the concentration, you increase the collisions, and increase the reaction rate

10 Factor #3: Surface Area/Particle Size Surface area: the outside part or uppermost layer of something that is exposed to air The smaller the particle, the larger the surface area The larger the surface area, the more particles that are exposed to cause a collision If you decrease the particle size, you increase the surface area, increase the number of collisions, and increase the reaction rate

11 Factor #4: Pressure Pressure: the continuous physical force exerted on or against an object by something in contact with it This is shoving the same amount of particles into a smaller space This is very similar to increasing concentration decreasing the amount of space increases the likelihood of successful collision If you increase the pressure on GASES, you increase the amount of collision, and increase the reaction rate

12 Factor #5: Catalyst Catalyst: a substance that increases the rate of a reaction by lowering the activation energy barrier It is chemically unchanged in a reaction If you lower the energy needed to a reaction to happen, it can happen faster If you add a catalyst, you increase the reaction rate

13 Graphical Relationships If you increase temperature, concentration, surface area, pressure, or add a catalyst, the reaction rate increases exponentially (curve not straight)

14 Graphical Relationships (cont) Here is a comparison of how much product is actually produced based on a higher temperature vs. a lower temperature You can replace temperature with high/low concentration, high/low surface area, with/without a catalyst, high/low pressure and the curves would look very similar

15 Copy down and fill out the chart below for homework (first one is done for you) Factor Definition Description (how it works) Relationship to Reaction Rate 1. Temperature A measure of the kinetic energy of particles in a substances 2. Increasing the temperature causes the particles to move faster, and more likely to collide with each other to form products Increase temperature, increase reaction rate