Question

A 100 g piece of granite and a 100 g piece of lead are placed in an oven that is at 100°C. The initial temperature of the pieces are 25°C. After a couple of minutes, neither one is at 100°C, but which one is warmer? Which one will reach 100°C first? How much energy will it take for both of the objects to reach 100°C?

Answer 1

Ans. #1. Specific heat of graphite = 0.7069 J g^-10C^-1

            Specific heat of lead = 0.128 J g^-10C^-1

Note that specific heat of Pb is lower than that of graphite. So, Pb required relatively lesser amount of heat to increase the temperature of unit mass by 1⁰C.

Therefore, Pb will get warmed more rapidly than graphite and would reach 100.0⁰C first.

#2. Amount of heat gained by a substance is given by-

            q = m s dT                            - equation 1

Where,

q = heat gained or lost

m = mass

s = specific heat

dT = Final temperature – Initial temperature

# Heat required by Pb

Putting the values in equation 1-

q1 = 100.0 x (0.128 J g^-10C^-1) x (100.0⁰C – 25.0⁰C)

Hence, q1 = 960.0 J

# Heat required by Graphite

Putting the values in equation 1-

q2 = 100.0 x (0.7069 J g^-10C^-1) x (100.0⁰C – 25.0⁰C)

Hence, q2 = 5301.75 J

# Total heat required by both the substance, Q = q1 + q2

                                                            = 960.0 J + 5301.75 J

                                                            = 6261.75 J