ACSI HL Energetics & Thermochemistry 2022 (Teacher)

IBDP Chemistry HL/ Energetic s & Thermochemistry Page 1 Anglo − Chinese School (Independent) Year 5 (2022) IBDP Chemistry HL (IBDP syllabus Topic 5) 5.1 Measuring Energy Changes - Essential Idea: The enthalpy c hanges from chemical reactions can be calculated from their effe ct on the temperature of their surroundings. 5.2 Hess’ Law − Essential Idea: In chemical tr ansformations energy can neither be created nor destroyed (the firs t law of thermodynamics). 5.3 Bond Enthalpies − Essential Idea: Energy is abs orbed when bonds are broken and is released when bonds are formed. (IBDP syllabus Topic 15) 15.1 Energy Cycles − Essential Idea: The concept of the energy change in a single step reaction being equivalent to the summation of smaller steps can be applied to changes involving ionic compounds. 15.2 Entropy and Spontaneity − Essential Idea: A reaction is spontaneous if the overall transformation leads to an increase in total entropy (system plus surroundings). The direction of spontaneous change always increases the total entropy of the universe at the expense of energy available to do useful work. This is known as the second law of thermodynamics. TOPIC 5 Energetics & Thermochemistry TEACHER COPY – WITH SUGGESTED SOLUTIONS

IBDP Chemistry HL/ Energetics & Thermochemistry Page 2 5.1 Measuring energy changes Essential idea: The enthalpy changes from chemical reactions can be calculated from their effect on the temperature of their surroundings.  Nature of Science:  Fundamental principle—conservation of energy is a fundamental principle of science. (2.6)  Making careful observations—measurable energy transfers betwee n systems and surroundings. (3.1) Understandings:  Heat is a form of energy.  Temperature is a measure of the average kinetic energy of the particles.  Total energy is conserved in chemical reactions.  Chemical reactions that involve transfer of heat between the s ystem and the surroundings are described as endothermic or exothermic.  The enthalpy change (ΔH) for chemical reactions is indicated i n kJ mol−1.  ΔH values are usually expressed under standard conditions, giv en by ΔHθ, including standard states. Applications and skills:  Calculation of the heat change when the temperature of a pure substance is changed using q = mcΔT.  A calorimetry experiment for an enthalpy of reaction should be covered and the results evaluated. Guidance:  Enthalpy changes of combustion (ΔH θc) and formation (ΔHθf) should be covered.  Consider reactions in aqueous solution and combustion reaction s.  Standard state refers to the normal, most pure stable state of a substance measured at 100 kPa. Temperature is not a part of the definition of standar d state, but 298 K is commonly given as the temperature of interest.  Th