CO(g) + 2 H2(g) ⇄ CH3OH(g) DH < 0 The synthesis of CH3OH(g) from CO(g) and H2(g) is represented by t — Thermodynamics Chemistry Question

STEPS:

1. Identify the thermodynamic nature of the reaction:
The reaction equation is given as $\text{CO}(g) + 2\text{ H}_2(g) \rightleftharpoons \text{CH}_3\text{OH}(g)$ with an enthalpy change of $\Delta H < 0$. A negative enthalpy change ($\Delta H < 0$) means that the reaction is exothermic, meaning it releases a net amount of heat energy to the surroundings.
2. Apply the fundamental rules of chemical bonding and energy:
* Breaking bonds is always endothermic: Energy must be absorbed from the surroundings to overcome the attractive electrostatic forces holding atoms together in the reactant molecules.
* Forming bonds is always exothermic: Energy is released to the surroundings as new attractions are established and the product molecules transition into a lower, more stable potential energy state.
3. Set up the relationship between bond energies and enthalpy change ($\Delta H$):
Mathematically, the net enthalpy change of a reaction can be expressed in terms of these two competing energy processes:
$$\Delta H = \text{Energy absorbed to break reactant bonds} - \text{Energy released to form product bonds}$$
4. Compare the magnitudes of the energy terms:
Because the reaction is exothermic ($\Delta H < 0$), the value of the equation above must be negative. For the difference to be negative, the energy released during product bond formation must be strictly greater than the energy absorbed during reactant bond cleavage:
$$\text{Energy absorbed to break reactant bonds} < \text{Energy released to form product bonds}$$
5. Select the correct statement:
This relationship means that the energy absorbed as the bonds in the reactants are broken is less than the energy released as the bonds in the product are formed, which perfectly matches Option C.

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WHY_OTHERS_WRONG:

• Option A is incorrect: If the energy absorbed to break reactant bonds were greater than the energy released during product bond formation, the net enthalpy change ($\Delta H$) would be positive. This would describe an endothermic reaction, which contradicts the given fact that $\Delta H < 0$.
• Option B is incorrect: This option reverses the physical chemistry of chemical bonds. Energy is absorbed (not released) when bonds are broken, and energy is released (not absorbed) when bonds are formed.
• Option D is incorrect: Like Option B, this statement misrepresents the physics of chemical bonding. It incorrectly states that energy is released when bonds are broken and absorbed when bonds are formed.