Question

Two hundred grams of a substance requires 18.8 kJ of heat to raise its temperature from 25°C to 45°C. Use the table to identify the substance. q = mCT. Mass (m) is in grams. Temperature is in degrees Celsius.

water

ammonia

gasoline

air

Answer 1

we are asked in the question to determine the substance given the heat required to achieve the temperature change and the mass of the substance. In this case, Cp is equal to q/m ΔT. substituting, 18.8 kJ / 200 g /20 K equal to 4.7 J / g K. The closest is that of water which is 4.18 J / g K

Answer 2

Answer: ammonia

Explanation:

Heat capacity is the amount of heat required to raise the temperature of 1 gram of substance through $1^0C$.

$Q= m\times c\times \Delta T$

Q= heat gained= 18.8 kJ

m= mass of the substance = 200 g

c = heat capacity= ?  

$\Delta T={\text{Change in temperature}}=(45-25)^oC=20^0C$  

$18800J=200g\times cJ/g^oC\times 20^oC$

$c=4.7J/g^oC$

The heat capacity of water is $4.186J/g^oC$ ,ammonia is $4.7J/g^oC$, gasoline is $2.22J/g^oC$ and air is $0.718J/g^0C$.

Thus the correct answer is ammonia.