Why is skin scalded by steam

Water in the form of a gas is called steam . Two things happen concurrently when human skin comes into close contact with steam - it could happen, for example, when we get too close to a boiling kettle. Firstly, the flesh in contact with the steam gets burnt and hurts. Secondly, steam converts from its gaseous form to become liquid water. We say it condenses. We summarize the condensation reaction thus  

The condensation reaction is one of the simplest forms of a phase change, which we discuss in greater depth in Chapter 5. 

From Equation (3.1), which defines the changes to internal energy, A U for the process in Equation (3.2) is A[/(condensation) = water, p 

The word exothermic comes from two Greek roots thermo, meaning energy or temperature, and exo meaning outside or beyond. An exothermic process therefore gives out energy. 

We will use the word process here to mean any physical chemistry requiring a change in energy. 

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