Question

1. how does the change in energy of a chemical reaction predict whether or not the reaction will occur?
2. explain the role of enzymes and how they affect the chemical reactions of living things.

critical thinking

1. sep use models explain why a key that fits into a lock is a useful model for the function of enzymes.
2. sep construct an explanation explain how consuming an acid - neutralizing antacid might affect protein digestion. apply the concept of activation energy to support your explanation.

Explanation:

1. If the change in energy (Gibbs free - energy change, $\Delta G$) of a chemical reaction is negative, the reaction is spontaneous and likely to occur; if positive, it is non - spontaneous under the given conditions; if zero, the reaction is at equilibrium.
2. Enzymes are biological catalysts. They lower the activation energy of chemical reactions in living things, increasing the rate of these reactions without being consumed in the process.
3. The key - lock model is useful for enzymes because just as a specific key fits into a specific lock, each enzyme has a specific active site with a unique shape that binds to a specific substrate, similar to how a key fits into a lock.
4. Protein digestion in the stomach occurs in an acidic environment. Acid - neutralizing antacids raise the pH. Enzymes involved in protein digestion, like pepsin, have an optimal pH for activity. Raising the pH increases the activation energy for protein - digestion reactions as the enzymes are less effective, thus slowing down protein digestion.

Answer:

1. A negative Gibbs free - energy change ($\Delta G$) indicates a spontaneous reaction likely to occur; positive $\Delta G$ means non - spontaneous; $\Delta G = 0$ is equilibrium.
2. Enzymes are biological catalysts that lower activation energy, increasing reaction rates in living things.
3. Each enzyme has a specific active site (like a lock) that binds to a specific substrate (like a key).
4. Antacids raise stomach pH, increasing activation energy for protein - digestion reactions as enzymes are less effective, slowing digestion.