Topic 5 Energy Changes

Question 1

What happens if the products is the reaction have more energy than the original reactants?

Answer 1

They must have taken in the difference in energy between the products and reactants.

Question 2

What happens if the products store less energy than the reactants?

Answer 2

The excess energy is transferred to the surroundings during the reaction.

Question 3

Why does the overall amount of energy not change in reactions?

Answer 3

It is conserved- it can’t be created or destroyed.

Question 4

What is an exothermic reaction?

Answer 4

One which transfers energy to the surroundings usually by heating.

Question 5

How do you recognise an exothermic reaction?

Answer 5

This is shown by a rise in temperature.

Question 6

What is an example of an exothermic reaction?

🔥⛽️ , 🌈, 💧, ⛄️, 🥫, 🏃🏽‍♀️, 🚿, ❄️

Answer 6

Burning fuels
Neutralisation reactions 
Oxidisation reaction 
Hand warmers
Self heating cans
Respiration 
Condensation 
Freezing

Question 7

What is an endothermic reaction?

Answer 7

One which takes in energy from the surroundings.

Question 8

How is an endothermic reaction shown?

Answer 8

A fall in temperature.

Question 9

What are some examples of endothermic reactions?

🍋, ☃️, 🌱, ☀️, 🧣, ☄️

Answer 9

Reaction between citric acid and sodium carbonate
Melting
Photosynthesis
Evaporation 
Cold packs (not ice packs) 
Thermal decomposition

Question 10

What happens during a chemical reaction?

Answer 10

New bonds are formed and old bonds are broken.

Question 11

What happens when new bonds are formed?

Answer 11

Energy must be supplied.

Question 12

What sort of reaction is the formation of bonds?

Answer 12

An exothermic reaction.

Question 13

What happens when old bonds are broken?

Answer 13

Energy must be supplied.

Question 14

What sort of reaction is the breaking of bonds?

Answer 14

An endothermic process.

Question 15

What is the size of the energy like in an exothermic reaction?

Answer 15

The energy released by forming bonds is greater than the energy used to break them.

Question 16

What is the size of the energy like in an endothermic reaction?

Answer 16

The energy used to break the bonds is greater than the energy released by forming them.

Question 17

What are reaction profiles?

Answer 17

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.

Question 18

What does the reaction profile of an exothermic reaction look like?

Answer 18

The products are at a lower energy than the reactants.

Question 19

What does the difference in the height of the reactants and products in a reaction profile represent?

Answer 19

The energy change in reaction per mole.

Question 20

The greater the activation energy…

Answer 20

The more energy the reaction needs to start.

Question 21

What does an endothermic reaction profile look like?

Answer 21

The products are at a higher energy than the reactants.

Question 22

How can you calculate the overall bond energy change in a reaction?

Answer 22

Sum of the energies needed to break bonds in the reactants - the energy released when the bonds are formed in the products.

Question 23

How can you test the effect of acid concentration released in a neutralisation reaction between hydrochloride acid and sodium hydroxide?

Answer 23

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.