`DeltaH` for the combustion of a compound is:

Options

A. positive
B. zero
C. negative
D. may be positive or negative

Answer

To determine the value of `Delta H` for the combustion of a compound, we can follow these steps:

### Step 1: Understand the Definition of Enthalpy of Combustion
The enthalpy of combustion is defined as the change in enthalpy when one mole of a substance is completely burned in the presence of excess oxygen.

**Hint:** Remember that combustion requires excess oxygen to be classified as such.

### Step 2: Identify the Nature of the Combustion Process
Combustion is an exothermic process, meaning it releases heat. This is because the products formed (usually CO2 and H2O) are at a lower energy state than the reactants.

**Hint:** Exothermic reactions release energy, which is a key characteristic of combustion.

### Step 3: Determine the Sign of Delta H
Since combustion is an exothermic process, the change in enthalpy (Delta H) is negative. This indicates that energy is released into the surroundings.

**Hint:** For exothermic reactions, Delta H is always negative.

### Step 4: Example of a Combustion Reaction
For instance, consider the combustion of methane (CH4):
\[ \text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O} + \text{heat} \]
In this reaction, methane is burned in excess oxygen to produce carbon dioxide and water, along with the release of heat.

**Hint:** Always balance the combustion reaction to accurately reflect the stoichiometry.

### Step 5: Conclusion
Based on the understanding that combustion is an exothermic process, we conclude that the enthalpy change for the combustion of a compound is negative.

**Final Answer:** The value of `Delta H` for the combustion of a compound is negative.