One characteristic or property of all solids and liquids is something called the Specific Heat, abbreviated as Cv. This quantity represents the amount of heat required to raise or lower a given quantity (a gram or a Kilogram) by one degree. Water has an extremely high Specific Heat (1 calorie per gram per degree C). A rule of thermodynamics (the study of heat and heat transfer) is that when two objects are placed in contact, they will eventually reach thermal equilibrium. Energy (heat is a measure of energy in a substance) flows from the warmer object or liquid to the cooler one until they both reach the same temperature (equilibrium). When we mix liquids, this rule must be obeyed.
Acknowledgements: Thank you to Dr. J.R. Harkay author ofPhenomenal Physics for providing this student inquiry activity. Adapted from "The Seven Percent Solution: Mixing," an Inquiry Exercise by J. R. Harkay. See www.PhenomenalPhysics.com for more information on the complete Guided Inquiry Curriculum.