C7- Energy Changes

Question 1

Exothermic reactions

Answer 1

Release energy into the surroundings. Often heats up the surroundings.

Question 2

Endothermic reactions

Answer 2

Take in energy from their surroundings

Question 3

Example of an exothermic reaction

Answer 3

The burning of fuels such as the comustion of methane gas.

Question 4

Energy in the products of exothermic reactions

Answer 4

Less energy than the reactants

Question 5

Example of an Endothermic reaction

Answer 5

Thermal decomposition reactions e.g the decomposition of Calcium carbonate

Question 6

Energy in the products of Endothermic reactions

Answer 6

The products have more energy than the reactants

Question 7

Uses of Exothermic reactions

Answer 7

Chemical hand warmers use exothermic reactions to warm you up
Self heating cans also use exothermic reactions

Question 8

What are reusable hand warmers based on?

Answer 8

The formation of Crystals from solutions of a salt

Question 9

Uses of endothermic reactions

Answer 9

Chemical cold packs

Question 10

How do chemical cold packs work?

Answer 10

They usually contain ammonium nitrate and water
When ammonium nitrate dissolves it absorbs energy from its surroundings making them colder.

Question 11

What are reaction profiles?

Answer 11

Diagrams showing the relative amounts of energy contained in the reactants and the products.

Question 12

What is on the X axis of a reaction profile?

Answer 12

Progress of reaction

Question 13

What is on the Y axis of a reaction profile

Answer 13

Energy

Question 14

What is the unit that energy change is measure in ?

Answer 14

kJ/mol or Kilojoules per mole

Question 15

Exothermic reactions ( energy change during reaction)

Answer 15

More energy in reactants
Less energy in products
Difference in energy is the energy transferred to the surroundings

Question 16

Endothermic reactions (energy change during reaction)

Answer 16

Less energy in reactants
More energy in the products
The difference is the energy taken in from the surroundings.

Question 17

Activation energy

Answer 17

The minimum amount of energy needed before colliding particles of reactants have sufficient energy to cause a reaction

Question 18

What is bond energy?

Answer 18

The energy needed to break the bond between two atoms.

Question 19

The greater the difference in reactivity between the two metals used…. ( electrical cells and batteries)

Answer 19

The higher the voltage produced

Question 20

Chemical cell set up

Answer 20

Join two metals together by a wire and dip them into an electrolyte and electrons will flow through the wire from one metal to another

Question 21

How can some batteries be recharged?

Answer 21

The battery is connected to a power supply that reverses the reactions that occur at each electrode when the cell is discharging. This regenerates the original reactants.

Question 22

Benefits of hydrogen as a fuel

Answer 22

It burns well and produces no pollutants

Question 23

What are fuel cells?

Answer 23

These cells are fed with hydrogen and oxygen and produce water. Most of the energy released in the reaction is transferred to electrical energy.

Question 24

Advantages of hydrogen fuel cells

Answer 24

Do not need to be electrically recharged
No pollutants are produced
Can be a range of sizes for different uses

Question 25

Disadvantages of hydrogen fuel cells

Answer 25

Hydrogen is highly flammable
Hydrogen is sometimes produced for the cell by non-renewable sources
Hydrogen is difficult to store