How much heat is required to convert 50g of water at 100°C to steam at the same temperature? (Specific latent heat of vaporization of water = 2260 Jg-11)

Analyze the question: Water at 100°C is changing to steam at the same temperature. The temperature doesn't change, so all the heat goes into changing state. This is latent heat, not specific heat capacity.

Concept: The heat needed to change a substance's state at constant temperature is

Q = m × L

where m is the mass and L is the specific latent heat (here, of vaporization).

Solution:

• m = 50 g
• L = 2260 J/g (the "Jg-11" in the question is a typing error for Jg⁻¹)

Q = 50 × 2260 Q = 113,000 J Q = 1.13 × 10⁵ J

Checking the options:

• A (1.13 × 10⁻⁴ J) is far too small.
• B (1.31 × 10² J) and C (1.30 × 10⁴ J) don't match the calculation.
• D (1.13 × 10⁵ J) matches exactly.
• E (1.31 × 10⁶ J) is too large.

Tip: Because the temperature stays the same, there is no ΔT, so don't use mcΔθ. Whenever a question says "at the same temperature" or "at its boiling or melting point," use Q = mL. Also check your units: if L is in J/g, use mass in grams. If L is in J/kg, use kilograms.