pH is not a process. pH is a measure of reaction that mathematically reflects negative logarithm of the hydrogen ion concentration in solution. The reaction (acid, neutral or alkaline) is a physico-chemical characteristic. It means - the reaction has an impact on physical properties of measured environment as well as on chemical composition.
Please keep in mind, that pH is only defined for aqueos solutions. In all other cases you have to refer to other values, e.g. pKa.
Though we deal with pH as a measure of proton concentration, it is more generally a measure of proton activity and as such is defined in both aqueous and non-aqueous systems. For a brief discussion of the physical process of non-aqueous pH measurement, see Helmuth Galster. "pH Measurement: Fundamentals, Methods, Applications, Instrumentation". Weinheim: VCH Verlagsgesellschaft mbH; 1991, pages 61-63
Hydrogen ion concentration is pH which varies with temperature, I am confused, how can we classify it as chemical or physical.
First, we should define both terms: Chemical properties and Physical properties what they stand for?, we can simply define the both terms as follow: Physical Properties are the properties that do not change the chemical nature of matter (e.g. color, smell, freezing point, boiling point, melting point, infra-red spectrum, opacity, viscosity and density), However, Chemical properties are the properties that do change the chemical nature of matter (e.g. heat of combustion, reactivity with water, and electromotive force), Thus, pH is a chemical parameter.
The pH is the proton concentration of a system. In fact, the expression is deduced from the autoprotolysis constant of the water, Which represents a chemical process. On the other hand, there are several ways to measure the pH, some are chemical like titration and some are based on physical processes such as a glass electrode.
The variation of pH which temperature is reflected on the variation of the water autoprotolysis constant as a function of temperature. As any other equilibrium constant, they change as a function of the inverse of the absolute temperature (K) with a linear behaviour.
Kunal Garg, at first I would like to appreciate the way you started the discussion. :)
pH is the measurement of proton concentration which actually affects the chemical reaction. As far as the process of measurement is concerned, M. Farooq Wahab has described it nicely as both physical and chemical process. It could be done by seeing the ionic strength on litmus paper (chemical means) or done by using electrodes (physical means).
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. pH deals with both Physical Properties & Chemical properties.
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