C7 - Energy Changes
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Exothermic and endothermic reactions in terms of bonds?
Breaking bonds aBsorbs energy, forRming bonds Releases energy
D. Activation energy?
minimum energy required for a reaction to take place
What kind of reactions are neutralisation reactions?
exothermic
RQ. What equipment do you need to investigate temperature changes?
poly(styrene) cup and thermometer
RQ. Method for investigating temperature changes? safety? improvements?
• Record initial temperatures of reactants • mix reactants in cup • record max/minimum temperatures reached • Safety = goggles • improvements= lid for cup, stirring to get even distribution of heat
Uses of exothermic reactions? (2)
Chemical hand warmers, self-heating cans
3 main endothermic reactions?
Photosynthesis, hydrogen carbonate + acid (sherbet) , dissolving ammonium nitrate in water
Equation for reaction in self-heating cans?
calcium oxide + water -> calcium hydroxide
Uses of endothermic reactions?
Chemical cold packs
How do chemical cold packs work?
They contain ammonium nitrate and water, when ammonium nitrate dissolves, it absorbs energy from surroundings
D Bond energy?
Energy needed to break a bond between 2 atoms
What units are bond energies measured in?
kJ/mol
You can use bond energies to work out…
the energy change for most reactions
When new bonds are formed between atoms….
energy is released
Energy must be supplied to…
break chemical bonds