CHEMISTRY · Subjective · AP · Chemistry · Chemical Reactions · Chemical Reactions
Problem
Fresh milk is quickly cooled to 4∘C for storage. After several hours at room temperature, the same milk sours as lactose is converted to lactic acid by bacterial enzymes, giving the milk a sharp taste and curdled appearance.
Classify the cooling step and the souring step as physical or chemical changes, respectively, and justify each classification in one sentence.