11. Energy changes in chemical reactions Flashcards
What happens in terms of energy, when a chemical reaction occurs?
Energy is transferred to or from the surroundings
What is an exothermic reaction?
One which transfers energy to the surroundings
Examples of an exothermic reaction?
Combustion, Neutralisation, and many oxidation reactions
What is an endothermic reaction?
One which thats in energy from the surroundings
Examples of an endothermic reaction?
Thermal decomposition, they are also the base of some sports injury packs
If a reversible reaction is exothermic in one direction, what is it in the other direction?
Endothermic
What type of reaction is the reaction of hydrated copper sulphate to anhydrous copper sulphate?
Endothermic
How is the relative amount of energy released when substances burn measured?
Through Calorimetry
How do you carry out Calorimetry?
Put 50g of water in a Copper can and record its temperature
Weigh the spirit burner and lid
Put the spirit burner under the can, and light the wick
Heat the water, stirring constantly, until the temperature reaches about 50’C
Put out the flame using the burner lid, and measure the final temperature of the water
Weigh the spirit burner and lid again
Q = mc ΔT
Q = the heat energy transferred (joule, J)
m = the mass of the liquid being heated (grams, g)
c = the specific heat capacity of the liquid (joule per gram degree Celsius, J/g°C)
ΔT = the change in temperature of the liquid (degree Celsius, °C)
How can the amount of energy released by a chemical reaction in solution be measured?
It can be calculated from the measured temperature change of the solution when the reagents are mixed in an insulated container
Used for reactions of solids with water or neutralisation reactions
What do catalyst do in chemical reactions?
They provide a different pathway for chemical reactions that has lower activation energy
