Question

5. Two 10.00 g blocks absorb 10.00 J of heat each. One block is made of lead (Pb), and the other one of copper (Cu). How are the changes in their temperature ∆T(Pb) and ∆T(Cu) related, and why? Cs(Pb) = 0.128 J/(g· ◦C), Cs(Cu) = 0.385 J/(g· ◦C).

(A) ∆T(Pb) = 3.01∆T(Cu) because Cs(Cu) = 3.01Cs(Pb)

(B) ∆T(Pb) = 3.01∆T(Cu) because Cs(Pb) = 3.01Cs(Cu)

(C) ∆T(Cu) = 3.01∆T(Pb) because Cs(Cu) = 3.01Cs(Pb)

(D) ∆T(Cu) = 3.01∆T(Pb) because Cs(Pb) = 3.01Cs(Cu)

(E) ∆T(Pb) = ∆T(Cu) because of the same masses and amounts of heat

Answer 1

Cs(Pb) = 0.128 J/(g· ◦C). This indicates that 0.128 J heat energy is required to increase the temperature of a 1 gram Pb block by 1 degree celsius. Similarly, Cs(Cu) = 0.385 J/(g· ◦C) indicates that 0.385 J heat energy is required to increase the temperature of a 1 gram Cu block by 1 degree celsius.

10 J heat will increase the temperature of 10 g Pb block by 10/(0.128*10) celsius i.e. ∆T (Pb) = 7.812 celsius.

10 J heat will increase the temperature of 10 g Cu block by 10/(0.385*10) celsius i.e. ∆T (Cu) = 2.597 celsius.

Therefore, ∆T(Pb) = 3.01∆T(Cu) is the correct relationship. The amount of supplied heat energy (10 J) is same for same amount of Pb and Cu block (10 gram). But, due to the difference in Cs value [Cs(Cu) = 3.01Cs(Pb)], their temperature increases in different extent.

Thus, the correction is (A) ∆T(Pb) = 3.01∆T(Cu) because Cs(Cu) = 3.01Cs(Pb)