The amount of heat required to change the state of 1 kg of substance at constant temperature is called

Options

A. kilocal
B. calorie
C. specific heat
D. latent heat

Explanation

To solve the question, we need to understand the concept of heat transfer during a phase change of a substance. Here’s a step-by-step solution:

### Step 1: Understand the Concept of Heat Transfer
When heat is added to a substance, it can either increase the temperature of the substance or change its state (phase). The amount of heat required to change the state of a substance at constant temperature is a key concept in thermodynamics.

**Hint:** Think about what happens when you heat ice. It melts into water without changing temperature at that moment.

### Step 2: Identify the Phase Change
During a phase change, such as melting (solid to liquid) or boiling (liquid to gas), the temperature of the substance remains constant even though heat is being added. This heat is used to break the intermolecular forces holding the particles together in the solid or liquid state.

**Hint:** Remember that during melting, the temperature of ice remains at 0°C until all the ice has melted.

### Step 3: Define Latent Heat
The amount of heat required to change the state of 1 kg of a substance at constant temperature is known as **latent heat**. It is denoted by the symbol **L**. This heat is specific to the substance and the type of phase change occurring (e.g., latent heat of fusion for melting, latent heat of vaporization for boiling).

**Hint:** Consider how different substances have different amounts of heat required for phase changes.

### Step 4: Write the Formula
The relationship between the heat added (Q), mass (m), and latent heat (L) can be expressed by the formula:
\[ Q = mL \]
Where:
- \( Q \) = amount of heat added
- \( m \) = mass of the substance (in kg)
- \( L \) = latent heat (in J/kg)

**Hint:** This formula helps you calculate the heat needed for a phase change if you know the mass and the latent heat of the substance.

### Conclusion
Thus, the amount of heat required to change the state of 1 kg of a substance at constant temperature is called **latent heat**.

**Final Answer:** Latent heat

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