5.2 Energetics
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What are the units of enthalpy change?
Delta H KJ/mol Either + or -
What is the enthalpy change:
Heat energy change per mole
what is the enthalpy change reaction between
reactants- products
What is an endothermic reaction
• Heat energy is taken in ( absorbed) • surrounding temperature decreases
What is an exothermic reaction
• heat energy is given out • surrounding temperature increase (gets hotter as heat energy has been released)
What sign is an endothermic reaction
+ positive as heat energy has been absorbed
What sign is an exothermic reaction
• negative as heat energy has been absorbed
Does breaking bonds absorb energy or release energy
Absorb energy
Does making bonds absorb energy or release energy
Release energy
Describe an energy level diagram for an endothermic reaction
heat energy is absorbed Delta H is positive Products have more energy so Products are higher than reactants
Describe an energy level diagram for an exothermic reaction?
Heat energy released Delta H negative Products end up with less energy Reactants are higher than Products
What is the equation for Delta H
Bonds broken- bonds made
What is the equation for Heat energy (Q)
Q= mc Delta T
what des each symbol stand for in the equation Q= mc delta T
Q= Heat energy M= mass C = 4.18 ( 4.2) Delta T= Temp change
What is the equation for Delta H
Delta H= -Q/ moles
What are two significant sources of error during a calorimetry experiment.
Heat Loss- Most of the heat energy dissipates into the air instead of the water Incomplete Combustion- Less energy released than expected Evaporation of water