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Energy Change & Chemical Reactions (Exothermic (Process (Chemical…
Energy Change & Chemical Reactions
Exothermic
Examples of Exothermic Reactions
Burning reactions; combustion of fuels
Detonation of Explosives
Reaction with acids and metals
defintion
Reaction in which heat is given out
You have to put heat in for boiling and melting
exothermic reactions start to lose heat.
Process
Chemical energy becomes heat energy
Eventually the reaction mixture gets hotter
evently heat is lost to surroundings
products have less chemical energy then reactants started with
ΔH
*ΔH is how much energy is given out
ΔH is negative because the products have less energy than reactants
The tempature of the surrondings increases
Endothermic
Definition
Reaction in which heat is taken in
enrgy must be supplied to break bonds
Enrgy releases when new bonds are made
ΔH
ΔH is postive because the products have more energy than the reactants
Endothermic Reactions
An endothermic reaction is one which takes in heat energy from the surroundings
The tempature of the surrondings decreases
Process
the reactants gain heat
Eventually the heat is absorbed from the surrondings and mixture returns to room temp.
Overall the chemicals have gained energy
Bond energy Values
C-H=435 KJ/Mol
O-H=464 Kj/Mol
O=O=497 KJ/Mol
C=O=803 KJ/Mol
C-O=360 KJ/Mol
C-C=346 KJ/Mol
Effects on the rate of Reactions
State of matter- In a Reaction between solid and an Aqueous/liquid/gas species, increasing the surface area of the solid-phase reactant increases the number of collisions per second and increases the reaction rate
Temperature- Increasing the tempature increases reaction rate because of disproportionately large increase in the number of high enregy collisions which result in a reaction.
Pressure- When increasing the presuure the molucules have less space they can move the greater density of molucules increases the number of collisions when decreasing presuure molucules dont hit as often and the reatction of rate decreases.
Surface Area- It exposes more of it particles to attack this creates a increased chance of collisions with reactant particles so there are more collisions in any given time Reaction rate increases
Concentration- When increased more molcules or ions interact to form new compunds and rate of reaction increases when concentratition decreases there are fewer molcules or ions and hte reaction of rate increases.
Catalysts & Inhibitors- Another way to control ther rate of reaction is to change the activation energy needed a catalyst inicreases the reaction rate by lowering the activation energy needed, they combine more easily and also changes equilibruim point.