Consider the reaction H2(g) + Br2(l) → 2 HBr(g). (b) Without doing a calculation, predict whether your estimate in part (a) is more negative or less negative than the true reaction enthalpy.

Verified step by step guidance

1. Step 1: Understand the reaction: The reaction given is H2(g) + Br2(l) → 2 HBr(g). This is a synthesis reaction where hydrogen gas reacts with liquid bromine to form hydrogen bromide gas.
2. Step 2: Consider the states of matter: Note that H2 is a gas, Br2 is a liquid, and HBr is a gas. The phase change from liquid to gas for Br2 will require energy input, which affects the enthalpy.
3. Step 3: Analyze bond energies: Breaking bonds requires energy, while forming bonds releases energy. In this reaction, the H-H and Br-Br bonds are broken, and new H-Br bonds are formed.
4. Step 4: Compare bond energies: Typically, the energy required to break the H-H and Br-Br bonds is less than the energy released when forming two H-Br bonds, suggesting an exothermic reaction.
5. Step 5: Predict the enthalpy change: Since the reaction is likely exothermic, the true reaction enthalpy is negative. If your estimate in part (a) did not fully account for the energy released in forming H-Br bonds, it might be less negative than the true reaction enthalpy.