1.

Explain the standard enthalpy of reactions.

Answer»

Solution :Enthalpy of a reaction depends on the conditions under which a reaction is CARRIED out. It is, THEREFORE, necessary that we MUST specify some standard conditions.
The standard enthalpy of reaction is the enthalpy change for a reaction when all the participating substances are in their standard STATES.
The standard state of a substance at a specified TEMPERATURE is its pure form at 1 bar.
For example, the standard state of liquid ethanol at 298 K is pure liquid ethanol at 1 bar , standard state of solid iron at 500 K is pure iron at 1 bar. Usually data are taken at 298 K.
Standard conditions are denoted by adding the superscript `Theta` to the symbol `Delta H `, e.g., `Delta H^(Theta)`


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