A warmer cup does not mean every energy change is positive — Physical Science: Chemistry

If a reaction transfers heat into surrounding water, the water’s heat is positive and the reaction-system heat is negative under the usual convention. A thermometer gives a temperature response, not an energy amount without a heat-capacity account. Include the cup, other material and environmental transfer where appropriate, and normalize by the actual reacting amount rather than an excess starting amount.

Breaking a specified bond costs energy. Product-bond formation can release more, making the complete reaction exothermic. Hess’s law combines state changes while scaling coefficients, phases and enthalpy consistently. A negative enthalpy does not by itself settle feasibility under every mixture, and a lower-energy product does not remove an activation barrier.

Entropy concerns accessible microscopic arrangements under physical constraints, beyond a visual disorder slogan. At constant temperature and pressure, a suitable Gibbs free-energy account combines enthalpy and entropy, while Q connects actual mixture composition to its standard reference. These tools explain direction and equilibrium; rate and practical performance still need pathway and measurement evidence.