Activation Energy

Definition

Activation energy is the minimum amount of energy required to initiate a chemical reaction. This energy barrier must be overcome for reactants to be transformed into products, impacting the reaction rate, extent of reaction, yield, and selectivity. A higher activation energy typically leads to a slower reaction rate, affecting how much product can be formed and how selective the reaction is toward specific pathways.

5 Must Know Facts For Your Next Test

1. Activation energy can be thought of as an energy hurdle that reactants must overcome to turn into products.
2. In reactions with high activation energies, fewer molecules have enough kinetic energy at lower temperatures to surpass this barrier, leading to lower yields.
3. The presence of a catalyst lowers the activation energy needed, allowing more reactant molecules to participate in the reaction and increasing both yield and selectivity.
4. Temperature affects activation energy indirectly; raising the temperature provides more energy to reactants, thus increasing the proportion that can overcome the activation barrier.
5. While activation energy is crucial for understanding how quickly a reaction occurs, it does not affect the position of equilibrium; it only influences how fast equilibrium is reached.

Review Questions

• How does activation energy impact the rate of a chemical reaction?
  • Activation energy significantly influences the rate of a chemical reaction because it determines how many molecules have sufficient energy to collide and react. A higher activation energy means fewer molecules can surpass this energy barrier at a given temperature, resulting in a slower reaction rate. Conversely, when activation energy is lowered, such as with a catalyst, more molecules are able to react, increasing the overall rate.
• Discuss the relationship between activation energy and yield in chemical reactions.
  • The relationship between activation energy and yield is important because higher activation energies can lead to lower yields of products. When reactants require more energy to start reacting, fewer molecules can overcome this barrier at lower temperatures. This results in less product formation over time. By using catalysts to lower activation energies, it's possible to increase yields by allowing more reactants to transform into products more efficiently.
• Evaluate how changes in temperature can affect activation energy and its implications for selectivity in chemical processes.
  • Changes in temperature affect the kinetic energy of molecules, which directly influences their ability to overcome activation energy. As temperature increases, more molecules have enough energy to surpass the activation barrier, potentially leading to faster reactions and different pathways being favored. This shift can impact selectivity because certain pathways may become more favorable than others when more reactants are able to react, changing the distribution of products formed in a chemical process.

Related terms

Catalyst: A substance that increases the rate of a chemical reaction by lowering the activation energy without being consumed in the process.

Reaction Rate: The speed at which reactants are converted into products in a chemical reaction, influenced by factors such as temperature, concentration, and activation energy.

Equilibrium Constant: A value that expresses the ratio of concentrations of products to reactants at equilibrium; influenced by thermodynamic parameters but not directly by activation energy.