chapter 11

Question 1

exothermic changes

Answer 1

-can be used in hand warmers and self heating cans
-crystallisation of a supersaturated solutuon is used in reusable warmers.
-however disposable one-off warmers can give off heat for longer

Question 2

endothermic changes

Answer 2

can be used in instant cold packs for sport injuries

Question 3

during a chemical reaction:

Answer 3

-energy must be supplied to break bonds
-energy is released when bonds are formed

Question 4

exothermic reaction bod=nds

Answer 4

the energy released from forming new bonds is greater than the energy needed to break existing bonds

Question 5

endothermic reaction bonds

Answer 5

the energy needed to break existing bonds is greater than the energy released from forming new bonds

Question 6

what is a chemical cell

Answer 6

-produces a potential diference until the reactants are used up

Question 7

fuel cells

Answer 7

-produce electricity through the reaction of a fuel with oxygen
-hydorgen-oxygen fuel cells use hydrogen as their fuel, and are useful in cars and spacecraft
-water is the only waste product from , so thye causes less pollution when in use

Question 8

benefits of hydrogen fuel cells

Answer 8

-dont need to be recharged
-no pollutants produced
-can be designed in a range of sizes for different uses

Question 9

disadvantages of hydrogen fuel cells

Answer 9

-hydorgen is high flammable
-sometime produced for the cell by non-renewable sources
-hydrogen is difficult to store

Question 10

the greater the difference…

Answer 10

in the reactivity of the two metals, the greater the voltage produced