Question

Сухое горючее(гексаметилентетрамин) обладает теплотой сгорания q=30 кДж/г. Сколько граммов сухого горючего потребуется для того,чтобы вскипятить Ь=200 г воды.Эффективность подогревателя n(ню)=40%,удельная теплоемкость воды с=4,2 Дж/г, температура в комнате t=20 c

Answer 1

Дано: m = 400г = 0,4кг; t1= 25 градС; t2 =40градС; Q= 1120 Дж; c - ?Решение. Количество теплоты, необходимое для нагревания тела, вычисляется по формуле Q = cm(t2 – t1); Отсюда удельная теплоемкость равна: c = Q/m(t2 – t1); Вычислим: c = 1120/0,4*( 40 – 15) = 112 (Дж/кг*град). 
Ответ: с = 112 Дж/кг*градС; 

Answer 2

To calculate the amount of dry fuel (hexamethylenetetramine) needed to boil 200 g of water, we can use the formula:

Q = m * c * ΔT

Where: - Q is the heat required to raise the temperature of the water - m is the mass of the water - c is the specific heat capacity of water - ΔT is the change in temperature

In this case, we want to find the mass of dry fuel (m) needed. We can rearrange the formula to solve for m:

m = Q / (c * ΔT)

Given: - Q = 30 kJ/g (heat of combustion of dry fuel) - m = ? - c = 4.2 J/g°C (specific heat capacity of water) - ΔT = boiling point of water - initial temperature

The boiling point of water is 100°C, and the initial temperature is 20°C. Therefore, ΔT = 100°C - 20°C = 80°C.

Now we can substitute the values into the formula and calculate the mass of dry fuel:

m = (30 kJ/g) / (4.2 J/g°C * 80°C)

Converting kJ to J and simplifying:

m = (30,000 J/g) / (4.2 J/g°C * 80°C)

m = 89.29 g

Therefore, approximately 89.29 grams of dry fuel (hexamethylenetetramine) would be required to boil 200 grams of water.

Please note that the efficiency of the heater (n) was not used in this calculation as it is not relevant to determining the mass of dry fuel required.