chemistry topic 5 Flashcards
(21 cards)
what happens during an exothermic reaction
An exothermic reaction transfers energy to the surroundings so the temperature of the surroundings increases
what happens during an endothermic reaction
An endothermic reaction is one that takes energy from the
surroundings so the temperature of the surroundings decreases
give examples of exothermic reactions
- Combustion
- Neutralisation
- Oxidation
give examples of endothermic reactions
- Thermal decomposition
- Sports injury packs
- Photosynthesis
what has to happen for a chemical reaction to take place
Chemical reactions can only occur when reacting particles collide with each other
with sufficient energy.
what is activation energy
The minimum amount of energy that particles must have to react is called the activation energy
compare the energy of reactants and products in exothermic reactions
Exothermic reactions
Reactants have MORE energy
than products
compare the energy of reactants and products in endothermic reactions
Endothermic reactions
Reactants have LESS energy
than products
whats the formula for overall energy change in a chemical reaction
Overall energy change =
Bonds broken – Bonds formed
Overall energy change = reactants - products
give definition of exothermic reactions
energy released from forming new bonds is greater than energy needed to break bonds
give definition of endothermic reactions
Energy needed to break bonds is
greater than energy released
from forming new bonds
describe Exothermic and endothermic reactions - REQUIRED PRACTICAL
- Add 25cm3 hydrochloric acid to beaker
- Measure initial temperature of acid
- Add a metal to acid
- Measure temperature change
- Repeat with other metals
- More reactive metals will have the highest temperature change
how do cells in batteries work
Cells contain chemicals which react to release electricity.
what does the voltage produced by a cell depend on
depends on the type of
electrode and electrolyte.
what are batteries
Batteries consist of two or more cells connected in series to
provide a greater voltage.
how can Rechargeable cells and batteries can be recharged
can be recharged if the chemical reactions are reversed
give features of non-rechargeable cells and batteries
-Cheap
-Only be used once
-Expensive in the long run
-Output falls gradually
-Toxic materials released when disposed
give features of rechargeable cells and batteries
-Expensive
-Used many times
-Cheap in the long run
-Output stays constant until flat
-Less toxic materials released when disposed
what do hydrogen fuel cells involve
hydrogen fuel cells involve the oxidation of hydrogen
to produce water.
advantages of using hydrogen fuel cells
Take less time to refuel than to recharge batteries
Can travel further before refuelling
Doesn’t produce toxic chemicals when disposed of
No CO2 produced
describe the process that make fuel cells work
Fuel cells work by using the
reaction between hydrogen
and oxygen to produce an
electric current:
1) The hydrogen atom loses
an electron (this is called
“oxidation”)
2) They then pass through
the electrolyte
3) The oxygen atoms gain two
electrons each
(“reduction”).
