HSC Chemistry 27 October 2023

Module 4:

DRivers of REactions

Drivers of Reactions

Students investigate factors that initiate and drive a reaction. They examine the relationship between enthalpy and entropy in calculating the Gibbs free energy. They also examine the roles that enthalpy and entropy play in the spontaneity of reactions. Students are provided with opportunities to understand that all chemical reactions involve the creation of new substances and associated energy transformations, which are commonly observable as changes in temperature of the surrounding environment and/or emission of light.

Students conduct investigations to measure the heat energy changes that occur in chemical reactions. They describe reactions using terms such as endothermic and exothermic, and explain reactions in terms of the law of conservation of energy. They use Hess’s Law to calculate enthalpy changes involved in the breaking and making of bonds.

Syllabus

Working Scientifically

develops and evaluates questions and hypotheses for scientific investigation CH11/12-1

analyses and evaluates primary and secondary data and information CH11/12-5

solves scientific problems using primary and secondary data, critical thinking skills and scientific processes CH11/12-6

communicates scientific understanding using suitable language and terminology for a specific audience or purpose CH11/12-7

Content

analyses the energy considerations in the driving force for chemical reactions CH11-11

Energy Changes in Chemical Reactions

IQ1: What energy changes occur in chemical reactions?

Students:

● conduct practical investigations to measure temperature changes in examples of endothermic and exothermic reactions, including:

– combustion

– dissociation of ionic substances in aqueous solution (ACSCH018, ACSCH037)

● investigate enthalpy changes in reactions using calorimetry and 𝑞 = 𝑚𝑐𝛥𝑇 (heat capacity formula) to calculate, analyse and compare experimental results with reliable secondary-sourced data, and to explain any differences

● construct energy profile diagrams to represent and analyse the enthalpy changes and activation energy associated with a chemical reaction (ACSCH072)

● model and analyse the role of catalysts in reactions (ACSCH073)

Enthalpy and Hess's Law

IQ2: How much energy does it take to break bonds, and how much is released when bonds are formed?

Students:

● explain the enthalpy changes in a reaction in terms of breaking and reforming bonds, and relate this to:

– the law of conservation of energy

● investigate Hess’s Law in quantifying the enthalpy change for a stepped reaction using standard enthalpy change data and bond energy data, for example: (ACSCH037)

– carbon reacting with oxygen to form carbon dioxide via carbon monoxide

● apply Hess’s Law to simple energy cycles and solve problems to quantify enthalpy changes within reactions, including but not limited to:

– heat of combustion

– enthalpy changes involved in photosynthesis

– enthalpy changes involved in respiration (ACSCH037)