Topic 5 Energy Changes Flashcards
What happens if the products is the reaction have more energy than the original reactants?
They must have taken in the difference in energy between the products and reactants.
What happens if the products store less energy than the reactants?
The excess energy is transferred to the surroundings during the reaction.
Why does the overall amount of energy not change in reactions?
It is conserved- it can’t be created or destroyed.
What is an exothermic reaction?
One which transfers energy to the surroundings usually by heating.
How do you recognise an exothermic reaction?
This is shown by a rise in temperature.
What is an example of an exothermic reaction?
🔥⛽️ , 🌈, 💧, ⛄️, 🥫, 🏃🏽♀️, 🚿, ❄️
Burning fuels Neutralisation reactions Oxidisation reaction Hand warmers Self heating cans Respiration Condensation Freezing
What is an endothermic reaction?
One which takes in energy from the surroundings.
How is an endothermic reaction shown?
A fall in temperature.
What are some examples of endothermic reactions?
🍋, ☃️, 🌱, ☀️, 🧣, ☄️
Reaction between citric acid and sodium carbonate Melting Photosynthesis Evaporation Cold packs (not ice packs) Thermal decomposition
What happens during a chemical reaction?
New bonds are formed and old bonds are broken.
What happens when new bonds are formed?
Energy must be supplied.
What sort of reaction is the formation of bonds?
An exothermic reaction.
What happens when old bonds are broken?
Energy must be supplied.
What sort of reaction is the breaking of bonds?
An endothermic process.
What is the size of the energy like in an exothermic reaction?
The energy released by forming bonds is greater than the energy used to break them.
What is the size of the energy like in an endothermic reaction?
The energy used to break the bonds is greater than the energy released by forming them.
What are reaction profiles?
Diagrams that show the relative energies of the reactants and products in a reaction, and how the energy changes over the course of a whole reaction.
What does the reaction profile of an exothermic reaction look like?
The products are at a lower energy than the reactants.
What does the difference in the height of the reactants and products in a reaction profile represent?
The energy change in reaction per mole.
The greater the activation energy…
The more energy the reaction needs to start.
What does an endothermic reaction profile look like?
The products are at a higher energy than the reactants.
How can you calculate the overall bond energy change in a reaction?
Sum of the energies needed to break bonds in the reactants - the energy released when the bonds are formed in the products.
How can you test the effect of acid concentration released in a neutralisation reaction between hydrochloride acid and sodium hydroxide?
1) Put 25 cm3 of 0.25mol/dm3 of hydrochloric acid and sodium hydroxide in separate beakers.
2) Place the beakers in a water bath set to 25 degrees Celsius until they are both at the same temperature.
3) Add the HCL followed by the NaOH to a polystyrene cup with a lid.
4) Take the temperature every 30 seconds for 5 minutes and the highest temperature.
5) repeat steps 1-4 using 0.5mol/dm3 and then 1mol/dm3 of hydrochloric acid.
