Which one of the following is always not negative

Options

A. Enthalpy of combustion
B. Enthalpy of formation
C. Enthalpy of neutralisation
D. Lattice enthalpy

Answer

To determine which type of enthalpy is always not negative, we need to analyze the four types of enthalpy mentioned: enthalpy of combustion, enthalpy of formation, enthalpy of neutralization, and lattice enthalpy.

### Step-by-Step Solution:

1. **Enthalpy of Combustion**:
- The enthalpy of combustion is the heat released when one mole of a substance is burned in oxygen.
- This process is exothermic, meaning it releases heat to the surroundings.
- Therefore, the enthalpy of combustion is always negative.

2. **Enthalpy of Formation**:
- The enthalpy of formation is the heat change that results when one mole of a compound is formed from its elements in their standard states.
- While many enthalpies of formation are negative (exothermic), there are exceptions. For example, the formation of certain compounds like nitrogen oxides or carbon sulfide can have a positive enthalpy of formation.
- Thus, the enthalpy of formation is not always negative.

3. **Enthalpy of Neutralization**:
- The enthalpy of neutralization is the heat change that occurs when an acid and a base react to form water and a salt.
- This reaction is also exothermic, resulting in the release of heat.
- Therefore, the enthalpy of neutralization is always negative.

4. **Lattice Enthalpy**:
- Lattice enthalpy refers to the energy released when gaseous ions combine to form an ionic solid.
- This process is exothermic as well, meaning that lattice enthalpy is also always negative.

### Conclusion:
Among the four types of enthalpy discussed, the **enthalpy of formation** is the only one that can be positive in certain cases, while the others (enthalpy of combustion, enthalpy of neutralization, and lattice enthalpy) are always negative. Therefore, the answer to the question is:

**Enthalpy of Formation** is the type of enthalpy that is always not negative.