Energy Changes

Question 1

What is enthalpy change?

Answer 1

The difference in energy between the products and the reactants.

Question 2

What is an exothermic reaction?

Answer 2

When energy is transferred to surroundings.

Question 3

What is an endothermic reaction?

Answer 3

When energy is taken in from surroundings.

Question 4

What type of reaction has a negative enthalpy change?

Answer 4

Exothermic reaction.

Question 5

What type of reaction has a positive enthalpy change?

Answer 5

Endothermic reaction.

Question 6

How can a graph show that a reaction is endothermic?

Answer 6

The energy of the product is greater than the energy of the reactants.

Question 7

What happens to bonds during a chemical reaction?

Answer 7

Bonds in reactants are broken.

Bonds in products are formed.

Question 8

In terms of bond energies, how is a reaction endothermic?

Answer 8

The energy released in forming bonds is less than the energy needed to break bonds.

Question 9

In terms of bonds formed or broken, how is the reaction exothermic?

Answer 9

More energy is released when bonds are formed than what is needed to break the bonds.

Question 10

What are 3 examples of exothermic reactions?

Answer 10

Combustion.

Oxidation reactions.

Neutralisation reactions.

Question 11

Respiration is an ___________ reaction.

Answer 11

Exothermic

Question 12

What is an every day product using endothermic reactions?

Answer 12

Ice-packs.

Question 13

What are 2 examples of endothermic reactions?

NOTE: 1 of these reactions are when compounds are broken into elements with a high temperature.

Answer 13

Photosynthesis and thermal decomposition.

Question 14

What do you do to calculate the mean value for maximum temperature after completing the experiment?

Answer 14

Repeat the experiment again to gain 2 sets of results.

Then calculate a mean value for the maximum temperature reached.

Question 15

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 ______________________.

Answer 15

volume

polystyrene cup

initial temperature

highest/ lowest temperature obtained

independent variable

Question 16

If the reaction of a solution is exothermic, will the temperature of the solution increase or decrease?

Answer 16

Increase.

Question 17

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.

Answer 17

greater volume

energy
spread out
greater volume

decreases

Question 18

You should use a polystyrene cup to __________ the mixture to stop unwanted ___________ through the sides and bottom.

Answer 18

Insulate

heat transfers

Question 19

You should put a ____ on the polystyrene cup to _____________________ to the air.

Answer 19

lid
reduce heat transfers

Question 20

Suggest why a solution was left for 4 minutes in room temperature before adding a metal:

Answer 20

To reach a constant temperature

Question 21

Explain why the temperature of a solution decreases
after being left for a few minutes after maximum temperature:

Answer 21

The reaction is complete.

So energy is lost to surroundings.