The thermal energy Q[J] of an object is defined as follows.
where c [J/(g K)] is the specific heat of the object.
Specific heat is the amount of heat required to raise the temperature of 1 gram of an object by 1°C.
Also, mc [J/K] is called heat capacity, which is the amount of heat required to raise the temperature of an object weighing "m" grams by 1°C.
■How to calculate heat quantity
Assume that the above substance has a mass of 100g and a temperature of 80°C.
It is not difficult to imagine that if this is left in a room at 20°C, the temperature will gradually drop to the same 20°C as the room.
Here, the temperature of the substance drops as heat quantity[J:joules] is exchanged between the substance and the gas in the room.
(Since the gas is given heat, the temperature rises, but here, the room is wide enough and the temperature is constant.)
How many joules is required to raise the temperature by 1°C ? The amount of heat Q when an substance is raised by ΔT℃ can be expressed as follows.
＜Difference between heat quantity and heat energy＞
The units of heat and heat energy are both joules, so you might think that they are the same, but heat energy refers to the total amount of heat that an substance has, and heat is the amount of work given to another substance.
■Relationship between joules and watts
There is a unit called watt [W] related to joule [J]. Watt is heat per hour. So joules are watts multiplied by time. Click here for related pages.
■heat quantity calculation example
＜Q1＞
Calculate the amount of heat lost when an substance with a mass of 100 g and a temperature of 80°C placed in a room equals the room temperature of 20°C. The specific heat of the substance is 0.435.
＜answer＞
(In this calculation, temperature is basically considered in Kelvin, but here ΔT is the same in both Kelvin and °C, so it is calculated in °C.)
＜Q2＞
Calculate the heat energy of the substance at 80℃ and 20℃.
＜answer＞
Here the temperature should be calculated in Kelvin. This difference in energy corresponds to the amount of heat lost in heat dissipation.
＜Q3＞
A heat of 1000J was applied to an substance at 20℃. how much does the temperature rise ?
■When considering temperature changes in time series
To consider temperature changes over time, it is necessary to solve differential equations. Click here.
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