The first law of thermodynamics states that:

• A. The enthalpy change of a reaction is independent of the pathway taken.
• B. Energy cannot be created or destroyed, only transformed from one form to another.
• C. The pressure and volume of a gas are inversely proportional at constant temperature.
• D. The entropy of a perfect crystal at absolute zero is zero.

Answer: (B)

Verified step by step guidance

1. Identify the statement that correctly represents the first law of thermodynamics. The first law is fundamentally about the conservation of energy.
2. Recall that the first law of thermodynamics can be expressed as the change in internal energy \(\Delta U\) of a system being equal to the heat added to the system \(q\) plus the work done on the system \(w\): \[\Delta U = q + w\]
3. Understand that this law implies energy cannot be created or destroyed, only transformed from one form to another, which is a key concept in thermodynamics.
4. Evaluate the given options against this principle: - The enthalpy change being independent of pathway relates to Hess's law, not the first law. - Pressure and volume being inversely proportional at constant temperature is Boyle's law, a gas law, not the first law. - The entropy of a perfect crystal at absolute zero is related to the third law of thermodynamics.
5. Conclude that the correct statement describing the first law of thermodynamics is: 'Energy cannot be created or destroyed, only transformed from one form to another.'