Energy Changes

Question 1

When talking about the temperature change in a reaction what do you need to make sure to write before the temperature?

Answer 1

+ and -

Question 2

Name two features of an endothermic reaction.

Answer 2

• Absorbing heat energy

- Decreases in temperature

Question 3

Name two features of an exothermic reaction.

Answer 3

• Releases heat energy

- Increases in temperature

Question 4

Why does an endothermic reaction have the two features it does?

Answer 4

Breaking the bonds in the chemical reaction requires more energy so the thermal energy is used to break the bonds. This in turn lowers the temperature.

Question 5

Why does an exothermic reaction have the two features it does?

Answer 5

The bonds being broken require heat energy, but during the reaction new bonds are made.
The energy released from forming new bonds is greater than the energy needed to break old bonds.

Question 6

Give examples of endothermic reactions.

Answer 6

• thermal decomposition
• photosynthesis
• electrolysis

Question 7

Explain in terms of bond breaking and making why this reaction is endothermic.

Answer 7

The reaction is endothermic because it absorbs heat energy decreasing the temperature, this occurs as bonds are being broken which requires heat energy. This is not an exothermic reaction because it doesn’t release heat energy increasing the temperature, this would occur as bonds are being broken which requires heat energy, but the energy released from forming new bonds is greater than the energy needs to break old bonds.

Question 8

What type of reaction goes on in a cool pack?

Answer 8

endothermic

Question 9

How does a cool pack work?

Answer 9

• A cool pack is made up of two bags, one containing water that is inside another that contains either ammonium nitrate, calcium ammonium nitrate or urea.
• When you squeeze the package the bag containing water breaks dissolving in the solid, this is an endothermic reaction so causes the pack to go cold.

Question 10

Why is a cool pack useful?

Answer 10

It relieves pain, swelling and inflammation from injuries and other conditions like arthritis.

Question 11

What type of reaction goes on in a self heating can?

Answer 11

Exothermic

Question 12

How does a self heating can work?

Answer 12

These make drinks like coffee hot without the need of an external heating device. The reaction used to transfer energy to the food or drink is…
calcium oxide + water→ calcium hydroxide
By pressing a button you break a seal to let them mix causing an exothermic reaction to occur.

Question 13

What type of reaction goes on in a hand warmer?

Answer 13

Exothermic

Question 14

How does a hand warmer work?

Answer 14

• This is an exothermic reaction used to warm people up in cold environments, they are also sometimes used to help ease aches and pains.
• Some hand warmers are re-usable, they are based on the formation of crystals from solutions of salt. The salt used is often sodium ethanoate (CH3COO-Na+). The supersaturated solution is prepared by dissolving as much salt as possible in hot water, the solution is then allowed to cool.
• A small metal disk is used to start the exothermic reaction, when you press it metal is scraped off that starts off the crystallisation.
• The reactions transfers heat energy to the surroundings.

Question 15

What are the reactants?

Answer 15

Two or more chemicals that react together to make a product.

Question 16

What are the products?

Answer 16

What is produced from a chemical reaction.

Question 17

what are successful collisions?

Answer 17

When reactant particles collide with enough energy to turn into products.