Energy from Reactions

Question 1

what is an exothermic reaction

Answer 1

when heat energy is given out to surroundings

Question 2

how do we know its an exothermic reaction

Answer 2

rise in temperature

Question 3

what happens to the energy of the products in an exothermic reaction

Answer 3

they have less energy than the reactants

Question 4

what is activation energy

Answer 4

minimum amount of energy needed by the reactant particles to react on collision

Question 5

what are some examples of exothermic reactions

Answer 5

combustion of fuels
neutralisation reactions
displacement reactions
respiration

Question 6

what is an endothermic reaction

Answer 6

when heat energy is taken in from the surroundings

Question 7

how do we know it is an endothermic reaction

Answer 7

drop in temperature

Question 8

what happens to the energy of the products in an endothermic reaction

Answer 8

they have more energy than the reactants

Question 9

what are some examples of endothermic reactions

Answer 9

electrolysis
cracking
photosynthesis

Question 10

what does a catalyst do

Answer 10

it provides an alternative reaction route that requires a lower activation energy. This speeds up the reaction because more of the reactant particles have enough energy to react on collision, so more successful collisions will occur

Question 11

what does it mean if the reaction is slow at room temperature

Answer 11

the reaction has a high activation energy

Question 12

why might one reaction take place faster than another is both are carried out under the same conditions

Answer 12

activation energy for one reaction is lower, so more of the reactant particles can react on collision

Question 13

is bond breaking endothermic or exothermic

Answer 13

endothermic, as energy is needed to break the bonds in the reactants

Question 14

is bond forming endothermic or exothermic

Answer 14

exothermic

Question 15

explain in terms of bond breaking and making why the reaction is exothermic

Answer 15

more energy is released when bonds are formed in the products than is needed to break bonds in the reactants. Therefore the reaction is overall negative and hence exothermic

Question 16

explain in terms of bond breaking and making why the reaction is endothermic

Answer 16

more energy is needed to break bonds in the reactants than is released when bonds are formed in the products. Therefore the reaction is overall positive and hence endothermic

Question 17

why must energy be supplied to start a reaction but it continues by itself once started

Answer 17

existing bonds must first be broken in the reactants before new bonds can form in the products. Bond breaking needs energy, whereas energy is released when new bonds are formed in the products. More energy is released when bonds are formed in the products, so the reaction is overall exothermic and provides the energy needed to break more bonds. Therefore the reaction continues

Question 18

why is hydrogen good fuel to use in an aeroplane

Answer 18

hydrogen has a low density
it gives out heat energy when burnt
combustion product is water which is not harmful

Question 19

Nickel sulphate water exists as bright green crystals and anhydrous nickel sulphate as a yellow powder.

How could you show that the action of heat on the hydrated salt is a reversible reaction

Answer 19

heat the green crystals in a test tube. The colour changes from green to yellow. Allow the test tube to cool, and then add water to the yellow powder. It turns green again.