if deltaH depends on temperature how can we define any reaction to be spontaneous or not on the basis of temperature only by gibbs energy also if any reaction is not carried out at constant pressure what value is to be put in in gibbs equation

Dear Student,

The mathematical expression for the gibbs free energy is expressed below,

$∆G=H-T∆S$
Whenever temperature increases the reaction will be exothermic as increased entropy condition favours spontaneous reaction with negative value of gibbs free energy.

In the last of statement it is given if the reaction is not considered to take part under constant pressure will result in endothermic reaction an non-spontaneous as the expanding pressure results in equilibrium temperature attainment with surroundings hence constant pressure too plays a vital role in achieving spontaneous reaction.