C7 - Energy Changes 1️⃣✅ Flashcards
What is an endothermic reaction?
An endothermic reaction is when energy is transferred from the surroundings during a reaction and the surroundings temperature falls
What is an exothermic reaction?
An exothermic reaction is when energy is transferred to the surroundings during an reaction and the surroundings temperature rises
What is a reaction profile?
A reaction profile is a graph that shows whether a reaction is exothermic or endothermic.
What is activation energy?
Activation energy is the minimum amount of energy that particles must have to react when they collide.
What does an endothermic reaction profile look like?
What does an exothermic reaction profile look like?
Breaking a bond requires ________ so is ____________
Breaking a bond requires energy so is endothermic
Making a bond ________ energy so is ___________
Making a bond releases energy so is exothermic
If a thermometer records an increase in temperature the reaction is ___________
exothermic
If a thermometer records a decrease in temperature the reaction is ____________
endothermic
In an endothermic reaction energy is transferred _______ the surroundings
In an endothermic reaction energy is transferred from the surroundings
In an exothermic reaction energy is transferred _______ the surroundings
In an exothermic reaction energy is transferred to the surroundings
What is bond energy?
The energy required to break a bond or the energy released when a bond is formed
In terms of bond breaking and making, what is an exothermic reaction?
Less energy is required to break the bonds than is released when making the bonds
In terms of bond breaking and making, what is an endothermic reaction?
More energy is required to break the bonds than is released when making the bonds
What is the equation used when doing bond energy calculations?
change = break - make
In bond energy calculations, if the change its negative it is ____________
Exothermic
In bond energy calculations, if the change its positive it is ____________
Endothermic
How do hydrogen fuel cells work?
- Hydrogen fuel is supplied to the -ve anode and is oxidised electrochemically, loosing its electrons, and cosequrntly setting up a potential difference across the cell (diffeerence in charge across the 2 electrodes) and resulting in generating electricity
- Hydrogen then becoms ions and travels through electrolyte to the +ve cathode where it and its electrons combine with oxygen to produce water.
- For every 1 oxygen atom, 2 hydrogen and 2 electrons are required to produce a water molocule
What is the half equation for the -ve anode in hydrogen fuel cells?
What is the half equation for the +ve cathode in hydrogen fuel cells?
What would the overall equation be to summarise a hydrogen fuel cell
REMEMBER: for evey 1 oxyen atom,2 hyrogen atoms is required to produce a water molocule hence for every 1 oxygen MOLOCULE you need 4 hydrogen atoms in order to produe a water molocule
How do rechargable cells/ batteries work?
Rechargeable cells and batteries can be recharged because the chemical reactions are reversed when an external electrical current is supplied.
How do non-rechargable batteries/ cells work?
In non-rechargeable cells and batteries the chemical reactions stop when one of the reactants has been used up
What is an example of a non-rechargable battery?
Alkaline battery
Electrodes in fuel cells are ____________ to electrodes in electrolysis
(give example)
Electrodes in fuel cells are opposite to electrodes in electrolysis
E.g.
Electrolysis: +ve anode & -ve cathode
Fuel cells: -ve anode & +ve cathode
What are the pros and cons to hydrogen fuel cells?
Pros:
* Only require hydrogen & oxygen
* No waste produces produced
* Last longer than batteries & are less poluting to dispose of
Cons:
* Because hydrogen is a gas takes up alot of space to store
* The hydrogen is dangerous to store as its explosive when mixed with air
* To make the hydrogen fuel, energy from fossil fuel fuesl is required
