Question

A 200 g piece of iron is heated to 100°C. It is then dropped into water to bring its temperature down to 22°C. What is the amount of heat transferred to water? (ciron = 0.444 J/g°C) A) 1.9 kJ B) 6.9 kJ C) 8.9 kJ Eliminate D) 10.9 kJ

Answer 1

The piece of iron is brought from a temperature of 100C to a temperature of 22C. In this process, the heat released by this piece of iron is
$Q=m C_s \Delta T$
where $m=200 g$ is the mass of the piece of iron, $C_s = 0.444 J/(g C)$ is the iron's specific heat, and the temperature variation is $\Delta T = 22^{\circ}-100^{\circ}=-78^{\circ}C$. Using these values, the amount of heat released by the iron is
$Q=(200 g)(0.441 J/(gC))(-78C)=-6926J=-6.9 kJ$
With negative sign because it is amount of heat released. This heat is then trasferred to the water, so the amount of heat absorbed by the water is Q=6.9 kJ.

Answer 2

The answer is B) 6.9 kJ.