Chemical reactions and chemical equilibrium

In a solution, equilibrium is the even mixing of solutes within a solvent. Solutes tend to move from areas of high concentration to areas of low concentration, leading to even dispersal of the solute in solution. Chemical reactions may also be in equilibrium. What does this mean?

Recall that chemical reactions can occur in two directions: forward and reverse. For example, the formation of carbonic acid is endergonic in the forward reaction and exergonic in the reverse reaction. Chemical equilibrium occurs when the forward reaction and the reverse reaction occur at the same rate. Special conditions are required to achieve chemical equilibrium for each reaction.

Inside of cells, most chemical reactions do not occur in conditions that favour chemical equilibrium. The special environment maintained within the cell ensures that some chemical reactions are irreversible, meaning that the reaction performed cannot convert the products back into the reactants. Most metabolic reactions are irreversible reactions. However, cells may change the intracellular environment to increase the rate of a reversible reaction in a particular direction. This is also true at the tissue, organ, and organ system level. For example, you will learn about how red blood cells, blood, and the respiratory system cooperate to ensure that carbon dioxide is effectively removed from the blood in a timely manner during our discussion of the respiratory system.

Cells change the conditions within the cell to affect whether certain chemical reactions will occur and how fast they will occur. This phenomenon is called regulation and you will examine this topic in nearly every lecture of this course.

Summary:

• Energy is the capacity to do work. It can be neither created nor destroyed and every energy transformation dissipates some energy as heat energy.
• A gradient is an uneven distribution of matter within a system.
• A potential is an uneven distribution of energy within a system.
• Cells use both chemical and electrical gradients, or electrochemical gradients, to store energy and prepare for the many energy transformations that sustain life.
• Chemical reactions rearrange matter
  • Endergonic chemical reactions require energy input to make/break bonds
  • Exergonic chemical reactions release energy as bonds are made/broken
• Chemical reactions achieve equilibrium when the rate of the forward and reverse reactions are approximately the same
  • The intracellular environment may favour one direction but the intracellular environment can change