Section 2: Heat The enthalpy change for a reaction is the enthalpy of the products minus the enthalpy of the reactants. K What I Know W What I Want to Find Out L What I Learned

11(E) Use calorimetry to calculate the heat of a chemical process. 11(D) Perform calculations involving heat, mass, temperature change, and specific heat. 11(B) Understand the law of conservation of energy and the processes of heat transfer. 11(C) Use thermochemical equations to calculate energy changes that occur in chemical reactions and classify reactions as exothermic or endothermic. 11(E) Use calorimetry to calculate the heat of a chemical process. Copyright © McGraw-Hill Education Heat

2(F) Collect data and make measurements with accuracy and precision. 2(G) Express and manipulate chemical quantities using scientific conventions and mathematical procedures, including dimensional analysis, scientific notation, and significant figures. 2(I) Communicate valid conclusions supported by the data through methods such as lab reports, labeled drawings, graphs, journals, summaries, oral reports, and technology–based reports. 3(A) In all fields of science, analyze, evaluate, and critique scientific explanations by using empirical evidence, logical reasoning, and experimental and observational testing, including examining all sides of scientific evidence of those scientific explanations, so as to encourage critical thinking by the student. Copyright © McGraw-Hill Education Heat

Essential Questions How is a calorimeter used to measure energy that is absorbed or released? What do enthalpy and enthalpy change mean in terms of chemical reactions and processes? Copyright © McGraw-Hill Education Heat

Vocabulary Review New pressure calorimeter thermochemistry system surroundings universe enthalpy enthalpy (heat) of reaction Heat Copyright © McGraw-Hill Education

Calorimetry A calorimeter is an insulated device used for measuring the amount of heat absorbed or released in a chemical reaction or physical process. Copyright © McGraw-Hill Education Heat

USING SPECIFIC HEAT Problem Response KNOWN mass of metal, m = 4.68 g Use with Example Problem 3. Problem A piece of metal with a mass of 4.68 g absorbs 256 J of heat when its temperature increases by 182°C. What is the specific heat of the metal? Could the metal be one of the alkaline earth metals listed in Table 2? KNOWN mass of metal, m = 4.68 g quantity of heat absorbed, q = 256 J ΔT = 182°C UNKNOWN specific heat, c = ? J/(g•°C) Response ANALYZE THE PROBLEM You are given the mass of the metal, the amount of heat it absorbs, and the temperature change. You must calculate the specific heat. Use the equation for q, the quantity of heat, but solve for specific heat, c. SOLVE FOR THE UNKNOWN State the equation for the quantity of heat, q. q = c × m × ΔT Solve for c. c = q m × ΔT Heat Copyright © McGraw-Hill Education

USING SPECIFIC HEAT SOLVE FOR THE UNKNOWN (continued) Substitute q = 256 J, m = 4.68 g, and ΔT = 182°C. c = 256 J (4.68 g)(182°C) = 0.301 J/(g•°C) Table 2 indicates that the metal could be strontium. EVALUATE THE ANSWER The three quantities used in the calculation have three significant figures, and the answer is correctly stated with three digits. The calculations are correct and yield the expected unit. Heat Copyright © McGraw-Hill Education

Chemical Energy and the Universe Thermochemistry is the study of heat changes that accompany chemical reactions and phase changes. The system is the specific part of the universe that contains the reaction or process you wish to study. The surroundings are everything else other than the system in the universe. The universe is defined as the system plus the surroundings. Copyright © McGraw-Hill Education Heat

Chemical Energy and the Universe Chemists are interested in changes in energy during reactions. Enthalpy is the heat content of a system at constant pressure. Enthalpy changes for exothermic reactions are always negative. Enthalpy changes for endothermic reactions are always positive. Enthalpy (heat) of reaction is the change in enthalpy during a reaction symbolized as ΔHrxn. ΔHrxn = Hfinal – Hinitial ΔHrxn = Hproducts – Hreactants Copyright © McGraw-Hill Education Heat

Chemical Energy and the Universe Copyright © McGraw-Hill Education Heat

Chemical Energy and the Universe Copyright © McGraw-Hill Education Heat

Review Essential Questions Vocabulary How is a calorimeter used to measure energy that is absorbed or released? What do enthalpy and enthalpy change mean in terms of chemical reactions and processes? Vocabulary calorimeter thermochemistry system surroundings universe enthalpy enthalpy (heat) of reaction Copyright © McGraw-Hill Education Heat