Question

energy diagram
energy
reaction progress
what does line c represent?
transition state
energy of the products
enthalpy of reaction
activation energy (forward)

Explanation:

Step1: Recall Energy Diagram Terms

In a chemical energy diagram, the enthalpy of reaction ($\Delta H$) is the energy difference between products and reactants. The vertical line C here shows the energy change from reactants to products (since reactants are lower, products higher, so it's the enthalpy change, or enthalpy of reaction). Let's analyze options:

• Transition state: The peak, not a vertical line.
• Energy of products: A horizontal line (the final energy level), not vertical.
• Activation energy (forward): The energy from reactants to transition state (peak), vertical but from reactants to peak, not reactants to products.
• Enthalpy of reaction: The energy difference between products and reactants, which is the vertical line C (reactants' energy to products' energy difference).

Step2: Match with Option

The vertical line C represents the enthalpy of reaction (energy change of the reaction, $\Delta H$), as it's the difference between products' and reactants' energy.

Answer:

enthalpy of reaction (the option: enthalpy of reaction)