To determine which statement applies to the given chemical system at dynamic equilibrium at 500 K, we need to understand the concept of dynamic equilibrium in the context of chemical reactions.
### Dynamic Equilibrium
1. Dynamic Equilibrium Definition:
- In a chemical system at dynamic equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction. This means the products are formed at the same rate at which they are consumed to form the reactants.
2. Characteristics of Dynamic Equilibrium:
- The concentrations of the reactants and products remain constant over time.
- Both the forward and reverse reactions continue to occur, but their rates are equal, so there is no net change in the concentration of reactants and products.
### Analysis of the Given Statements:
1. "The forward and reverse reactions no longer occur.":
- This statement is incorrect. At dynamic equilibrium, both the forward and reverse reactions continue to occur, but at equal rates.
2. "The rates of the forward and reverse reactions are unequal.":
- This statement is incorrect. At dynamic equilibrium, the rates of the forward and reverse reactions are equal.
3. "The concentrations of the products and reactants do not change.":
- This statement is correct. At dynamic equilibrium, the concentrations of the reactants and products remain constant because the rates of the forward and reverse reactions are equal.
4. "The forward reaction stops at 500 K.":
- This statement is incorrect. The forward reaction does not stop; it continues to occur, but its rate is equal to that of the reverse reaction at equilibrium.
### Conclusion
Based on the explanation above, the correct statement that applies to the given chemical system at dynamic equilibrium at 500 K is:
"The concentrations of the products and reactants do not change."
Thus, the correct answer is the third statement.
