we add 100 ml of water at 20 degrees celcius to 10g of an unknown substance which is at 50 degrees celcius. The water ends up at 25 degrees celcius. how much heat was transfered?

M*C*(delta T)

= 100 g * (water specific heat) * (temperature change of the water)

= 100 * 1.00 * 5.0 = 500 calories

The temperature of the unknown subtance doesn't matter, but you could use it to determine its heat capacity.