Given at
`A(s) to A(l), DeltaH =x`
`A(l) to A(g), DeltaH =y`
The heat of sublimation of A will be

Options

A. `x-y`
B. `x+y`
C. x or y
D. `-(x+y)`

Answer

To find the heat of sublimation of substance A, we can analyze the given reactions and their associated enthalpy changes. Here’s the step-by-step solution:

### Step 1: Understand the given reactions
We have two reactions:
1. \( A(s) \rightarrow A(l) \) with \( \Delta H = x \) (this is the process of melting or fusion).
2. \( A(l) \rightarrow A(g) \) with \( \Delta H = y \) (this is the process of evaporation or boiling).

### Step 2: Define sublimation
Sublimation is the process where a solid turns directly into a gas without passing through the liquid phase. Therefore, to find the heat of sublimation, we need to consider the transformation from solid A directly to gas A.

### Step 3: Combine the reactions
To achieve the sublimation of A, we can combine the two reactions:
- Start with the solid \( A(s) \) and convert it to liquid \( A(l) \) using \( \Delta H = x \).
- Then, convert the liquid \( A(l) \) to gas \( A(g) \) using \( \Delta H = y \).

When we add these two reactions together, we get:
\[ A(s) \rightarrow A(l) \rightarrow A(g) \]

### Step 4: Calculate the total enthalpy change
The total enthalpy change for the sublimation process is the sum of the enthalpy changes of the two steps:
\[ \Delta H_{\text{sublimation}} = \Delta H_{\text{melting}} + \Delta H_{\text{vaporization}} \]
Thus,
\[ \Delta H_{\text{sublimation}} = x + y \]

### Final Answer
The heat of sublimation of A is:
\[ \Delta H_{\text{sublimation}} = x + y \]

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