NSW Syllabuses

# Chemistry Stage 6 - Year 11 - Module 4: Drivers of Reactions Module 4: Drivers of Reactions

## Outcomes

#### A student:

• CH11/12-1

develops and evaluates questions and hypotheses for scientific investigation

• CH11/12-5

analyses and evaluates primary and secondary data and information

• CH11/12-6

solves scientific problems using primary and secondary data, critical thinking skills and scientific processes

• CH11/12-7

communicates scientific understanding using suitable language and terminology for a specific audience or purpose

• CH11-11

analyses the energy considerations in the driving force for chemical reactions

## Content Focus

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.

## Working Scientifically

In this module, students focus on developing questions and hypotheses to analyse trends, patterns and relationships in data in order to solve problems and communicate scientific understanding of ideas about the driving forces in chemical reactions. Students should be provided with opportunities to engage with all the Working Scientifically skills throughout the course.

## Content

• ### Energy Changes in Chemical Reactions

• Inquiry question: 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 $$q = mc\Delta T$$ (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

• Inquiry question: 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)
• ### Entropy and Gibbs Free Energy

• Inquiry question: How can enthalpy and entropy be used to explain reaction spontaneity?
• Students:
• analyse the differences between entropy and enthalpy
• use modelling to illustrate entropy changes in reactions
• predict entropy changes from balanced chemical reactions to classify as increasing or decreasing entropy
• explain reaction spontaneity using terminology, including: (ACSCH072)
• Gibbs free energy
• enthalpy
• entropy
• solve problems using standard references and $$\Delta G^\circ = \Delta H^\circ - T\Delta S^\circ$$ (Gibbs free energy formula) to classify reactions as spontaneous or nonspontaneous
• predict the effect of temperature changes on spontaneity (ACSCH070)