Dafuq

Chapter 1: THERMOCHEMISTRY

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physical chemistry-CHM431- Dr noraini hamzah

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Contents:

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Exothermic and endothermic reactions. Energy profile. Enthalpy and enthalpy change. Calorimetry. Heat capacity and specific heat. Definition of heat of reaction and calculations. Hess”s law and calculation.

physical chemistry-CHM431- Dr noraini hamzah

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DEFINITION

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Thermochemistry is the study of the energy changes taking place during chemical reactions.

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physical chemistry-CHM431- Dr noraini hamzah

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INTRODUCTION

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Every substance contains stored chemical energy, called enthalpy, mainly by virtue of chemical bonds.

Absolute enthalpy is hard to measure, but enthalpy changes during reactions are easy to measure because there will be an observable energy exchange between the chemicals and the surroundings. Energy cannot be created or destroyed, but can change from one form to another.

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Exothermic and Endothermic Reactions

Every reaction can be considered as a series of bond breaking steps followed by bond forming steps. Bond breaking always requires energy. All bonds have different 'strengths' of energies.

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Exothermic and Endothermic Reaction (cont.)

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If bond forming releases more energy than was required in the bond breaking, then overall energy is released to the surroundings i.e. an exothermic reaction ( H = negative) If bond forming releases less energy than was required in the bond breaking, then overall energy will have been absorbed from the surroundings i.e. an endothermic reaction ( H = positive).

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A chemical system and its surroundings.

the surroundings

the system

9/13/2013 8:18 AM physical...