The specific heat capacity of a substance is an intrinsic property that describes how much heat energy is required to raise the temperature of a unit mass of that substance by one degree Kelvin (o

The boiling point of water is $100 ^\circ\text{C}$.

$$\Delta T = T_{final} - T_{initial}$$ $$\Delta T = 100 ^\circ\text{C} - 20 ^\circ\text{C}$$ $$\Delta T = 80 ^\circ\text{C}$$

The formula for heat energy is $Q = mc\Delta T$.
Given:

• Mass of water ($m$) = $1.5 \text{ kg}$
• Specific heat capacity of water ($c$) = $4200 \text{ J/kg K}$ (or $\text{J/kg }^\circ\text{C}$)
• Change in temperature ($\Delta T$) = $80 ^\circ\text{C}$

Substitute the values:

$$Q = (1.5 \text{ kg}) \times (4200 \text{ J/kg }^\circ\text{C}) \times (80 ^\circ\text{C})$$ $$Q = 6300 \text{ J/}^\circ\text{C} \times 80 ^\circ\text{C}$$ $$Q = 504000 \text{ J}$$

Power ($P$) is the rate at which energy is transferred, so $P = \frac{Q}{t}$.
Rearrange to solve for $t$: $t = \frac{Q}{P}$.
Given:

• Power ($P$) = $2 \text{ kW} = 2000 \text{ W}$ (since $1 \text{ kW} = 1000 \text{ W}$)
• Heat energy ($Q$) = $504000 \text{ J}$

Substitute the values:

$$t = \frac{504000 \text{ J}}{2000 \text{ W}}$$ $$t = 252 \text{ s}$$

The correct option is A.

$$\boxed{\text{A. } 252 \text{ s}}$$

21. The statement "The increase in the internal energy of a system is equal to the heat added to the system plus the work done on the system" is the definition of the First Law of Thermodynamics. This law is a statement of the conservation of energy.

The correct option is A.

$$\boxed{\text{A. First Law of Thermodynamics}}$$