Chapter U5, Problem 5STP

Interpretation Introduction

Interpretation:

The best description of the final temperature when 100 ml of water at 20 ^oC is mixed with 50 mL of water at 80 ^oC needs to be identified from the given options.

Concept introduction:

Chemical reactions in general involve exchange of heat between the system (reactants and products) and the surroundings. The heat (q) absorbed or evolved is given as: $\text{q = m ×c×ΔT ------(1)}$

Here, m and c are the mass and specific heat capacity of the substance and ΔT = change in temperature = T_final-T_initial

Answer to Problem 5STP

Option (B).

Explanation of Solution

Since the density of water is 1 g/ml, 100 mL of water would be equivalent to 100 g and 50 mL would correspond to 50 g of water.

From equation (1), the amount of heat absorbed or evolved is directly proportional to the mass of the system. Therefore, 100 mL of water which has a higher mass would require more heat to reach a higher final temperature. As a result, the final temperature would be less than 50 ^oC.

Conclusion

The final temperature will be less than 50 ^oC since the 100 mL sample has a higher volume.