Parts of an Energy Diagram

• Energy Diagram: A diagram that shows the energy needed, the transition state, and the products as a reaction takes place.
• Transition State: Is a state between the reactants and products.
• Activation Energy: The energy required for a chemical reaction to occur. If the activation energy is not reached, no reaction will happen. Also, this is the energy between the reactants and the transition state.
• Reactants:
  • The chemicals you combine
  • What you start with​
  • Chemicals before the arrow
• Products:
  • The things that are being produced
  • The result of the reaction
  • The chemicals after the arrow
• Reaction Rate: ∆[reactant or product]/∆time

Watch the following video.

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Concentration of Ingredients and Hamburgers

Lets say you want to make a hamburger, and to make one hamburger, you need the following ingredients:

• 1 hamburger patty
• 1 hamburger bun
• 1 slice of cheese

How many hamburgers can you make if you have the following ingredients: 5 hamburger patties, 5 hamburger buns and 5 slices of cheese?

• Answer: 5 Hamburgers ​
  

​​If you use the ingredients (reactants) listed above to make the hamburgers (products), will you have any ingredients (reactants) leftover?

• Answer: No

As you make hamburgers (products), the amount of ingredients (reactants) decreases, but the amount of hamburgers increases. The same thing will happen in a chemical reaction. In a chemical reaction, as the reaction proceeds the concentration of reactants decreases as they are used up. Also, as the reaction proceeds, the concentration of products increases as they are created.

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Collision Reactions and Collision Theories

Chemical reactions are similar to a demolition derby.

• Lots of cars (molecules/atoms) are racing around an enclosed space running into each other.
• The cars (molecules/atoms) are moving at different speeds and collisions happen at different speeds and at different angles (orientation).
  • The orientation and speed at which these collisions happen determine how much damage is done to a car, or if a chemical reaction will take place.

Collision Theory

• Particles must collide
• There must be sufficient energy
• The particles must have the correct orientation when they hit each other.

Watch the following video to learn about collision theory.

https://youtu.be/wbGgIfHsx-I

Speed of Molecules

The speed of molecules is related to how much energy a molecule has.

• The faster a molecule is moving, the more energy it has.
• If the reaction is to proceed, the molecules must collide with enough energy to form the transition state.
• So, the faster molecules are moving, the more likely they are to collide with enough energy for the transition state to form.

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Activation Energy

Instead of thinking about individual collisions, let’s think about a reaction as a whole, with LOTS of molecules colliding. Remember, temperature is measure of average kinetic energy of the molecules at that temperature. Some molecules are moving faster, others are moving slower. This means that if a reaction requires a temperature of 50⁰C to proceed, some molecules will have enough energy, some will not

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Catalyst

Emma Ambrogi, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons

• Catalyst:  A substance which increases the rate of a chemical reaction, by decreasing the activation energy, without taking part in the chemical reaction
  
  • Since the activation energy is lowered, it is easier for molecules to collide with enough energy, so the reaction proceeds faster.
    
• Enzymes are a type of catalyst commonly found in the human body
  
  • We NEED enzymes to survive!  Many vital chemical reactions in our body would take place MUCH too slow without the help of enzymes
    
  • Example:  An enzyme called Pepsin helps to break down proteins in our stomach
    

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Let's Review

Watch the following video from 0:00 to 2:55!

https://youtu.be/fEXq_RvnYgI