Equal masses of paraffin and water are mixed in a container of negligible thermal capacity. Initial temperature of water is 80C and that of paraffin is 20 0C. The final temperature of mixture is:
Correct answer: C. 500C
- A. 700C
- B. 600C
- C. 500C
- D. 400C
Explanation
Since the container has negligible thermal capacity, the heat lost by the hot water (80°C) will be equal to the heat gained by the cold paraffin (20°C). The heat exchange can be calculated using the principle of calorimetry:m₁ * c₁ * (Tf - T₁) = m₂ * c₂ * (T₂ - Tf)where:m₁ = mass of waterc₁ = specific heat capacity of waterTf = final temperature of the mixtureT₁ = initial temperature of waterm₂ = mass of paraffinc₂ = specific heat capacity of paraffinT₂ = initial temperature of paraffinSince the masses of paraffin and water are equal, m₁ = m₂. Also, since the container is negligible in thermal capacity, c₁ ≈ c₂.Using this information, we get:m * c * (Tf - 80) = m * c * (20 - Tf)Tf - 80 = 20 - Tf2 * Tf = 100Tf = 50°C
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About Thermal Equilibrium and Heat
Thermal equilibrium means that bodies in contact have the same temperature and no net heat flows between them. The topic distinguishes heat from temperature, uses the zeroth law of thermodynamics, and covers heat transfer, specific heat capacity, thermal expansion and the conditions for reaching equilibrium.
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