Flashcards in Energy Deck (16):
What happens whenever chemical reactions occur?
There are changes in energy (heat or cool).
What can we measure?
The amount of energy released by a chemical reaction (in solution).
How can we measure the amount of energy released by a chemical reaction?
-By taking the temperature of the reagents (making sure they are the same).
-Mixing them in a polystyrene cup.
-And measuring the temperature of the solution at the end of the reaction.
What is the biggest problem with energy measurements?
The amount of energy lost to the surroundings.
How can you reduce the amount of energy lost to the surroundings when measuring the amount of energy released?
-By putting the polystyrene cup into a beaker of cotton wool to give more insulation.
-And by putting a lid on the cup to reduce energy loss by evaporation.
What else does this method work for?
-Reactions of solids with water
What is an example of this method to measure the amount of energy released by a chemical reaction?
-Put 25cm cubed of dilute hydrochloric acid in a polystyrene cup, and record its temperature.
-Put 25cm cubed of dilute sodium hydroxide in a measuring cylinder and record its temperature.
-If they are the same add the acid to the alkali and stir.
-Take the temperature of the mixture every 30 seconds, and record the highest temperature it reaches.
When else can this method be used?
Where energy is being absorbed, as the temperature will fall instead of rising.
What are reactions either?
What is an exothermic reaction?
One which gives out energy to the surroundings, usually in the form of heat and usually shown by a rise in temperature.
What is an endothermic reaction?
One which takes in energy from the surroundings, usually in the form of heat and usually shown by a fall in temperature.
What happens during a chemical reaction to the bonds?
-New bonds are formed.
-Old bonds are broken.
What happens when new bonds are formed?
Energy is released, so bond formation is an exothermic process.
What happens when old bonds are broken?
Energy must be supplied, so bond breaking is an endothermic process.
What happens in an exothermic reaction?
The energy released in bond formation is greater than the energy used in breaking old bonds.