Hess’ Law OCR AS Chemistry

Enthalpy changes bundle OCR AS Chemistry

This bundle is ideal for classroom or home learning and covers all of the OCR A level chemistry specification section 3.2.1 − enthalpy changes. The energetics topics covered are enthalpy changes, experimental determination of enthalpy changes, bond enthalpies and Hess’ Law. Each topic includes a fully interactive PowerPoint including starter, group activities, questions and plenary along with a worksheet. Answers to all exercises are provided. Some of the resources include a PowerPoint quiz. This bundle is part of a series covering the OCR AS Chemistry specification and relates to the following section: Module 3 – Periodic table and energy / Part 2 – Physical chemistry / 3.2.1 Enthalpy changes Content covered: **Enthalpy changes** • What is enthalpy • Law of conservation of energy • Enthalpy change • Enthalpy profile diagrams • System and surroundings • Exothermic and endothermic reactions and examples • Activation energy • Standard enthalpy changes • Standard conditions • Definitions of enthalpy changes • Simple calculations involving enthalpy changes **Experimental determination of enthalpy changes** • Energy exchange with the surroundings - heat loss in a chemical system = heat gain by surroundings • Temperature scales • Determining enthalpy changes using calorimetry • Calculations involving q = mc∆T . • Determining enthalpy changes in solution • Determining enthalpy of combustion • Errors associated with calorimetry experiments and how to minimise them • Cooling curves and how to find the temperature rise • Thermometric titration **Bond enthalpies** • Making covalent bonds (exothermic) and breaking covalent bonds (endothermic) • Overall enthalpy change linked to relative enthalpies of breaking and making bonds – enthalpy profile diagram • Average bond enthalpies and why they differ from actual bond enthalpies • Factors affecting average bond enthalpies • Calculations involving bond enthalpies • Limitations of bond enthalpy calculations • Plenary discussion about why there is a constant increase in the enthalpy change of combustion of alcohols for each CH2 group added **Hess’ Law** • Hess’ Law • Indirect determination of enthalpy changes • Enthalpy cycles • Calculating enthalpy changes from enthalpy changes of combustion • Calculating enthalpy changes from enthalpy changes of formation • Summary of types of enthalpy calculation • Calculating enthalpy changes from unfamiliar enthalpy cycles **Links** Next lesson: Topic 29 – Rates of reaction and collision theory (in preparation) Free resource - standard form, decimal places and significant figures https://www.tes.com/teaching-resource/resource-12405507