Question

5 l of water at 60°C is mixed with 25 l of water at 20°C. What is the final temperature of water?​

Answer 1

Use the “lever rule” or method of moments. Imagine they are weights on either end of a beam and you have to have a fulcrum to balance. Obviously the 1 litre should be 5 times as far away from the fulcrum as the 5 litre. That is, the fulcrum is 5/6 of the way from the l liter to the 5 litre.

The length between them is 20 degrees, so the fulcrum is 5/6 x 20 degrees from the temperature of the 1 litre towards the temperature of the 5 litre.

In this case, it is 30 + 16.67 degrees.

Works for other kinds of mixing, including concentrations.

E.g. if we had 1 litre of 30 g/l and 5 litres of 50 g/l, the concentration would be 46.67 g/l.

Very quick, easy and handy thing to know in chemistry.

Answer 2

Answer:

Final Temprature=26.67 degree Celsius

Explanation:

if you want you can exclude the specific heat capacity of water =4186J/kg°C and then solve the question