Chapter 4
- Created by: AHillSeeks11
- Created on: 05-02-18 12:34
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- Chapter 4 Summary
- Hess's Law
- The chemical change for a chemical reaction is the same whatever route is taken
- Flame Calorimeter
- Improved version of simple calorimeters used for measuring enthalpy changes of combustion
- Following features reduce heat loss futher: fuel burns in pure oxygen rather than air
- Example of a Formation
- Example of Combustion
- Bond enthalpy
- Bond dissosciation enthalpy: defined as the enthalpy change required to break a covalent bond with all species in gaseous state
- Mean bond enthalpy: same bond may have slightly different bond enthalpies in different molecules
- Thermochemistry
- when chemical reactions take place chemical bonds break and new bonds form
- Energy given out in a reaction is exothermic
- Energy taken in a reaction is endothermic
- Enthalpy change
- When you measure a heat change at a constant pressure
- Standard conditions for measuring enthalpy change are: pressure of 100kPa and temperature of 298k
- Exothermic and Endothermic reactions
- Neutralising an acid with an alkali = Exothermic reaction
- Break down of limestone to lime and carbon dioxide = Endothermic reaction
- Standard Enthalpies
- Standard molar enthalpy of formation
- The enthalpy change when 1 mole of a substance is formed from its elements in standard states under standard conditions
- Standard molar enthalpy of combustion
- The enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions
- Standard molar enthalpy of formation
- Enthalpy level diagrams
- Measuring the enthalpy change of a reaction.. 3 things need to know
- Mass of the substance that is being heated
- Temperature change
- Specific heat capacity of a substance
- Hess's Law
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