The standard Gibbs energy of formation of the product C(g) is -8.4 kJ/mol (this value is negative!) at 25 'C. Find the new reaction Gibbs energy (in J/mol) when the partial pressures of A, B and C are 7, 4 and 11 bar, respectively

Which of the following is an indication that a substance has undergone a chemical change? a. no new product has been formed. b. the color of the substance has not changed. c. the original constitute has not changed. d. the molecular structure has changed.