Question

What is the amount of heat required to raise the temperature of 100 g of water from 30°C to 80°C? (Specific heat of water = 4.2 J/g°C)

• A. 2,100 J
• B. 12,600 J
• C. 21,000 J
• D. 42,000 J

Hint:

Use \( Q = mc\Delta T \) for heat calculations. Make sure mass is in grams, specific heat is in J/g°C, and temperature change is calculated correctly as final minus initial.

Answer 1

The Correct Option is C

The heat energy \( Q \) required to change the temperature of a substance is calculated using the formula:
\[ Q = mc\Delta T \]
Where:
\( Q \) represents heat energy in joules.
\( m \) is the mass of the substance in grams.
\( c \) is the specific heat capacity.
\( \Delta T \) is the change in temperature.

Procedure:
Step 1: Identify given values.
\( m = 100 \, \text{g} \)
\( c = 4.2 \, \text{J/g°C} \)
\( \Delta T = 80^\circ C - 30^\circ C = 50^\circ C \)
Step 2: Apply the formula.
\[ Q = 100 \times 4.2 \times 50 = 21,000 \, \text{J} \]
Conclusion: The heat energy needed is 21,000 joules.