If a mixture contains 75% of one compound and 25% of its enantiomer what is the e. e

The enantiomeric excess (ee) of a mixture is an indicator of the compound's purity. A 50/50 (racemic) mixture has an ee of 0% while a single enantiomer has an ee of 100%. Therefore, take the major enantiomer compound in the mixture, 75%, and subtract its minor enantiomer contributor, 25%, to get an ee of 50%.

Yes it would be a physical change.