C7 Energy changes Flashcards
What is the 1st thermodynamics?
Energy cannot be created or destroyed
What happens to the total amount of energy in the universe
At the end of the chemical reaction it is the same as before the reaction takes place.
What happens in bond breaking and bond making
The bond takes in heat from its surroundings and breaks them apart.
Then the heat that is taken in is released into the surroundings and this creates new bonds
What is an exothermic reaction ?
An exothermic reaction is one that releases heat energy to the surrounding so the temperature of the surrounding increase.
What are examples of exothermic reaction
Neutralisation Oxidation e.g respiration Displacement reaction Burning Hot food Hot water
What is an endothermic reaction?
An endothermic reaction is on that takes in energy from the surroundings so the temperature of the surroundings decrease
What are examples of endothermic reaction?
Thermal decomposition Electrolysis Baking soda Photosynthesis Instant ice pack
What are example reactions for exothermic reaction?
CaCO3(s)—> CaO(s) + O2(g)
What is an example reaction of endothermic reaction
2HCL(aq) + Mg(s)—> MgCl2 (aq) + H2(g)
How much kJ/mol to break H-H -+>2H
It takes 436KJ/MOL
How do you work out the overall energy change
Overall energy change = energy used to break bonds - energy released on making new bonds
Calculate the overall energy change for the reaction
Explain why and how it is an endothermic or exothermic reaction.
3192- 3234 = -42KJ/mol
More energy is released when new bonds are formed when the reactant bonds are broken
Exothermic
Calculate the overall energy change for the reaction
Explain why and how it is an endothermic or exothermic reaction.
732- 628 = + 104 KJ/mol
Less energy is released when new bonds are formed when the reactant bonds are broken
