Question

Какое кол-во теплоты отдает кусок железа массой 3кг при остывании от 300 до 20 градусов цельсия? Объясни почему в ответе знак "-"?

Answer 1

Q = cm(t2-t1)
где c - удельная теплоемкость железа = 460 Дж\кг*С
Q = 460 * 3 (20-300) = - 386,4 кДж

Минус несет чисто физический смысл. Минус нам даёт понять, что теплота выделяется в окружающую среду. 

Answer 2

Calculating Heat Release from Iron

To calculate the amount of heat released by a piece of iron as it cools from 300°C to 20°C, we can use the formula:

Q = mcΔT

Where: - Q = heat released - m = mass of the iron (3 kg) - c = specific heat capacity of iron - ΔT = change in temperature (300°C - 20°C)

Specific Heat Capacity of Iron

The specific heat capacity of iron is approximately 0.449 J/g°C or 449 J/kg°C.

Calculation

Substitute the given values into the formula: Q = 3 kg * 449 J/kg°C * (300°C - 20°C)

Q = 3 kg * 449 J/kg°C * 280°C

Q = 376,200 J

So, the amount of heat released by the 3 kg piece of iron as it cools from 300°C to 20°C is 376,200 Joules.

Explanation for the Negative Sign

The negative sign in the answer indicates that heat is being released from the iron as it cools. When heat is released from a system, the change in internal energy is negative, which is why the negative sign is used in the formula for heat transfer. It signifies the direction of heat flow, which in this case is from the iron to the surroundings as it cools down.

I hope this explanation helps! If you have further questions or need additional information, feel free to ask.