THE PRINCIPLES OF ENERGY 51 



would be no transference of heat, no matter what quantity of 

 hot water were in, circulation. Heat of itself flows from a 

 hotter to a colder region — that is, there must be a difference of 

 intensity in order that the flow may occur. 



Why does a chemical reaction occur ? Why, for instance, do 

 coal gas and oxygen combine, of themselves, to form carbonic 

 acid gas and water ? The reaction is (assuming that the gas is 

 CH4 — that is, marsh gas; it really contains hydrogen and other 

 inflammable substances) : 



CH4+202=C02+2H,0, 



and the reaction occurs as if the equation were written from 

 left to right. Why from left to right, and not from right to left ? 

 Marsh gas and oxygen combine to form carbonic acid and water, 

 because in doing so a large quantity of heat is evolved; but if 

 CO2 and H,0 are to combine, a large quantity of heat (or more 

 generally of energy) must be given to them, or be absorbed by 

 them. Therefore they do not combine of themselves, although 

 they can be made to do so. Chemical reactions occur, as a rule, 

 , only if heat is evolved, and so we may predict the occurrence if 

 we know that heat may be generated. We cannot enter into the 

 qualifications of this statement, but it may be made more general 

 • by saying that a chemical transformation will occur if in the 

 occurrence work will be done. That is " why " it occurs, and 

 if no work can be done by the chemical substances by reacting 

 with each other they will not react of themselves. 



And if work is done as the result of the occurrence of a trans- 

 , formation energy will be dissipated, for all work done tends to 

 transform into heat. But, again, all heat generated tends to 

 distribute itself by conduction, radiation, and convection. It 

 t cannot of itself accumulate in one place, as it tends to become 

 uniformly diffused throughout the system — the room, the world, 

 and, finally, the whole universe. And so our experience is that 

 in all transformations energy becomes dissipated — that is, 

 intensity differences become levelled down. Therefore we say 

 that an energy transformation occurs of itseK if energy can be 

 dissipated, or if intensity differences can be abolished. 



This is the sign of the transformation. Marsh gas and oxygen 

 react with the evolution of heat and the production of carbonic 

 acid and water. But CO2 and OH2 do not react with the pro- 

 duction of marsh gas, because heat would be absorbed in this 



