Energy Changes Flashcards
What is enthalpy change?
The difference in energy between the products and the reactants.
What is an exothermic reaction?
When energy is transferred to surroundings.
What is an endothermic reaction?
When energy is taken in from surroundings.
What type of reaction has a negative enthalpy change?
Exothermic reaction.
What type of reaction has a positive enthalpy change?
Endothermic reaction.
How can a graph show that a reaction is endothermic?
The energy of the product is greater than the energy of the reactants.
What happens to bonds during a chemical reaction?
Bonds in reactants are broken.
Bonds in products are formed.
In terms of bond energies, how is a reaction endothermic?
The energy released in forming bonds is less than the energy needed to break bonds.
In terms of bonds formed or broken, how is the reaction exothermic?
More energy is released when bonds are formed than what is needed to break the bonds.
What are 3 examples of exothermic reactions?
Combustion.
Oxidation reactions.
Neutralisation reactions.
Respiration is an ___________ reaction.
Exothermic
What is an every day product using endothermic reactions?
Ice-packs.
What are 2 examples of endothermic reactions?
NOTE: 1 of these reactions are when compounds are broken into elements with a high temperature.
Photosynthesis and thermal decomposition.
What do you do to calculate the mean value for maximum temperature after completing the experiment?
Repeat the experiment again to gain 2 sets of results.
Then calculate a mean value for the maximum temperature reached.
What are the steps in the temperature changes in reacting solutions practical? (5)
Measure an appropriate ___________ of solution and mass of the solid.
Place solution in the ________________.
Record _________________ of solution.
Add solid and record the ______________________________.
Repeat experiment and increase the ______________________.
volume
polystyrene cup
initial temperature
highest/ lowest temperature obtained
independent variable
If the reaction of a solution is exothermic, will the temperature of the solution increase or decrease?
Increase.
Once the energy released has hit its maximum, as there is a _______________ of solution,
the more _________ that is released will ____________ into the _________________.
So the maximum temperature _____________ after this point.
greater volume
energy
spread out
greater volume
decreases
You should use a polystyrene cup to __________ the mixture to stop unwanted ___________ through the sides and bottom.
Insulate
heat transfers
You should put a ____ on the polystyrene cup to _____________________ to the air.
lid
reduce heat transfers
Suggest why a solution was left for 4 minutes in room temperature before adding a metal:
To reach a constant temperature
Explain why the temperature of a solution decreases
after being left for a few minutes after maximum temperature:
The reaction is complete.
So energy is lost to surroundings.
