endothermic & exothermic

Question 1

what is an exothermic reaction?

Answer 1

a chemical reaction that releases energy (usually as heat or light) to the surroundings.
Temperature increases.

Question 2

what does “exo” mean?

Answer 2

out - hence releasing energy into the surroundings.

Question 3

what is an endothermic reaction?

Answer 3

a chemical reaction that absorbs energy from the surroundings.
Temperature decreases.

Question 4

what does “endo” mean?

Answer 4

in - takes in heat/absorbs energy.

Question 5

how can you tell if a reaction is exothermic?

Answer 5

• surroundings get warmer because
  heat is released.
• the released energy is greater than
  the activation energy.

Question 6

how can you tell if a reaction is endothermic?

Answer 6

• surroundings get colder because
  heat is absorbed
• the released energy is less than the
  activation energy.

Question 7

examples of an exothermic reaction

Answer 7

• burning wood or gas
• fireworks exploding
• hand warmers

Question 8

examples of an endothermic reaction

Answer 8

• photosynthesis (plants using
  sunlight)
• melting ice
• instant cold packs

Question 9

is boiling water endothermic or exothermic?

Answer 9

endothermic – it absorbs heat to turn liquid into vapour.

Question 10

is freezing water endothermic or exothermic?

Answer 10

exothermic – heat is released as water turns to ice.

Question 11

what happens during a chemical reaction in terms of bonds?

Answer 11

bonds in reactants are broken, and new bonds in products are formed.

Question 12

does breaking bonds require or release energy?

Answer 12

requires energy — it takes energy to break bonds.
(endothermic process)

Question 13

does making bonds require or release energy?

Answer 13

releases energy — forming bonds gives off energy.
(exothermic process)

Question 14

when is a reaction exothermic in terms of bonds?

Answer 14

when more energy is released in forming new bonds than is used to break old ones.

Question 15

when is a reaction endothermic in terms of bonds?

Answer 15

when more energy is used to break bonds than is released in making new ones.

Question 16

what is activation energy?

Answer 16

the minimum energy needed to start a chemical reaction by breaking the initial bonds.

Question 17

is activation energy needed in both exothermic and endothermic reactions?

Answer 17

yes — all chemical reactions need activation energy to get started.

Question 18

example of a reaction with high activation energy

Answer 18

combustion — needs a spark or flame to begin
(e.g. lighting a match)

Question 19

what is chemical energy?

Answer 19

chemical energy is the energy stored in the bonds between atoms in a substance

Question 20

what happens to chemical energy in an exothermic reaction?

Answer 20

chemical energy is released to the surroundings — usually as heat or light.
- temp is hotter

Question 21

what happens to chemical energy in an endothermic reaction?

Answer 21

chemical energy is absorbed from the surroundings to break bonds.
- temp is colder