Bond Enthalpies
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- Created on: 15-05-19 09:45
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- Bond Enthalpies
- What are bond enthalpies?
- Energy needed to break a bond
- Have specific values that differ
- depending on which atoms are attached on either side of bond
- Breaking & Making Bonds
- When reactions happen, reactant bonds are broken & product bonds are formed
- Need energy to break bonds
- bond breaking is endothermic (enthalpy change +)
- stronger bonds take more energy to break
- Energy is released when bonds form
- bond forming is exothermic (enthalpy change -)
- Enthalpy change for the reaction is overall effect of making & breaking the bonds
- if you need more energy to break bonds than released when bonds are made - enthalpy change is +, if less its -
- Mean Bond Enthalpies
- Energy required to break bond can change depending on where it is
- In calculations we use mean bond enthalpies
- average energy needed to break certain type of bond, over range of compounds
- often given in data tables & used in calculations
- Calculating Enthalpy Changes
- Enthalpy change of reaction = total energy absorbed - total energy released
- Calculate total energy needed to break bonds in reactants
- usually be given average bond enthalpies for each type of bond
- multiply each value by number of each bond present
- usually be given average bond enthalpies for each type of bond
- Find total energy released by reaction
- calculate total energy needed to form all new bonds in products
- use average bond enthalpies
- calculate total energy needed to form all new bonds in products
- Different Types of Enthalpy Change
- Standard enthalpy change of formation
- enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions
- Standard enthalpy change of combustion
- enthalpy change when 1 mole of substance is completely burned in oxygen under standard conditions with all reactants and products in their standard state
- Standard enthalpy change of reaction
- enthalpy change when a reaction occurs in molar quantities shown in chemical equation, under standard conditions with all reactants & products in their standard state
- Standard enthalpy change of formation
- What are bond enthalpies?
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