energy changes

Fuel cells convert the chemical energy in a fuel and oxygen into:

electricity

which direction do the electrons flow in a hydrogen-oxygen fuel cell?

from the anode to the cathode

what is an electrolyte?

a solution through which ions can flow

what are the electrodes in hydrogen- oxygen fuel cells made from?

porous carbon which has lots of tiny holes and a catalyst to speed up the reaction

what are the main advantages of hydrogen-oxygen fuel cells?

- hydrogen and oxygen are both renewable

- the reaction doesn’t produce any pollutants after disposal

- fuel cells last longer than batteries

what are the main disadvantages of hydrogen-oxygen fuel cells?

- hydrogen is highly explosive and flammable, so a danger to store

- hydrogen is a gas so it requires a large space to store

- hydrogen requires energy to be made (using fossil fuels) which are non renewable energy resources

- expensive to make due to high cost of catalysts

how does a hydrogen fuel cell work?

1. hydrogen comes in from the left inlet into the anode and is oxidised (loses electrons) to become hydrogen ions and this sets up a potential difference across the cell

2. the electrons pass along the wire to the cathode, then the hydrogen ions move through the electrolyte to the cathode

3. then the electrons and hydrogen ions react with oxygen to make water so oxygen is reduced ( gains electrons)

4. water then leaves the fuel cell by the outlet and the process is complete

what is the half equation at the anode?

H_{2 ——> 2H⁺ + 2e^-}

what is the half equation at the cathode?

O₂ + 4H⁺ +4e^- ——> 2H₂O

what is the overall equation for a hydrogen-oxygen fuel cell?

O₂ + 2H₂ ——> 2H₂O

how is a cell made?

by connecting two different electrodes ( cathode and anode) with a wire and placing them in contact with an electrolyte, there will also be a voltmeter so that you can measure the voltage of the cell

what is an electrolyte?

a liquid through which ions can flow

what are batteries?

two or more cells connected in series to provide a greater voltage

what three factors affect the voltage of a cell?

1. the metals used for the electrodes - greater difference in reactivity, the greater the voltage will be

2. type and concentration of electrolyte used

3. conditions such as temperature and pH

what makes a good electrolyte

it should be able to conduct electricity and carry ions, so it must be liquid and ideally be an ionic compound to conduct electricity

how does temperature of the electrolyte affect the rate of reaction?

higher temperature increases the rate of collision so in turn increases the rate of reaction

how does the concentration of the electrolyte affect the reaction?

higher concentration increases the likelihood ( rate of collision) as there are more particles per unit of volume so the particles are closer together/less space between the particles so there are a greater number of collisions

what’s the difference between electrolysis and chemical cells?

electrolysis uses electricity to cause a chemical reaction whereas chemical cells use chemical reactions to produce electricity

what are rechargeable cells?

Rechargeable cells are cells and batteries that can be recharged because the chemical reactions are reversed when an external electrical current is supplied

what are some uses of rechargeable cells?

mobile phones and laptops

what are some uses of non rechargeable cells?

alkaline batteries, remote controls, kids toys, smoke alarms

what are non rechargeable cells?

in non rechargeable cells and batteries the chemical reactions stop when one of the reactants has been used up so a voltage is no longer produced, so there is no longer any flow of electrons so the cell stops producing electricity

what are endothermic reactions?

reactions that absorb energy from their surroundings

what are exothermic reactions?

reactions that transfer/release energy to the surroundings usually in the form of heat

what are some examples of an endothermic reaction?

- Photosynthesis

- Melting ice

- Evaporation of water

what are some examples of an exothermic reaction?

- Combustion

- Rusting of iron

- Neutralization reactions

- Respiration

is the reactants higher or lower than the products on a reaction profile for endothermic reactions? Explain a reason for your answer

lower, as energy is absorbed so the products have a higher energy level than the reactants

are the reactants higher or lower than the products on a reaction profile for an exothermic reaction? Explain a reason for your answer

higher, as energy is released to the surroundings so the products have a lower energy level than the reactants

what is activation energy?

the minimum amount of energy the reactant particles need in order to collide with each other and react

the greater the activation energy the _____ energy that will be required to start the reaction

more

how do you find out the overall energy change from a reaction profile?

the line from the reactants to the products

how do you find out activation energy from a reaction profile?

the difference in energy between the top of the curve/hump and the reactant

why do exothermic reactions release energy to the surroundings

because the energy released when forming binds is greater than the energy needed to break bonds

what is a bond energy?

the amount of energy required to break one mole of a particular covalent bond

what is the equation for overall energy change?

energy required to break bonds - energy released forming bonds

what type of reaction is forming bonds and why?

Forming bonds is an exothermic reaction because energy is released when new bonds are created, making the system more stable

what type of reaction is breaking bonds and why?

Breaking bonds is an endothermic reaction, as it requires energy input to overcome the bond energy and break the bonds, it also absorbs heat from the surroundings, making it endothermic.

how do you calculate energy needed to break a bond?

energy needed = moles x bond energy

Fuel cells convert the chemical energy in a fuel and oxygen into:

electricity

which direction do the electrons flow in a hydrogen-oxygen fuel cell?

from the anode to the cathode

what is an electrolyte?

a solution through which ions can flow

what are the electrodes in hydrogen- oxygen fuel cells made from?

porous carbon which has lots of tiny holes and a catalyst to speed up the reaction

what are the main advantages of hydrogen-oxygen fuel cells?

- hydrogen and oxygen are both renewable

- the reaction doesn’t produce any pollutants after disposal

- fuel cells last longer than batteries

what are the main disadvantages of hydrogen-oxygen fuel cells?

- hydrogen is highly explosive and flammable, so a danger to store

- hydrogen is a gas so it requires a large space to store

- hydrogen requires energy to be made (using fossil fuels) which are non renewable energy resources

- expensive to make due to high cost of catalysts

how does a hydrogen fuel cell work?

1. hydrogen comes in from the left inlet into the anode and is oxidised (loses electrons) to become hydrogen ions and this sets up a potential difference across the cell

2. the electrons pass along the wire to the cathode, then the hydrogen ions move through the electrolyte to the cathode

3. then the electrons and hydrogen ions react with oxygen to make water so oxygen is reduced ( gains electrons)

4. water then leaves the fuel cell by the outlet and the process is complete

what is the half equation at the anode?

H_{2 ——> 2H⁺ + 2e^-}

what is the half equation at the cathode?

O₂ + 4H⁺ +4e^- ——> 2H₂O

what is the overall equation for a hydrogen-oxygen fuel cell?

O₂ + 2H₂ ——> 2H₂O

how is a cell made?

by connecting two different electrodes ( cathode and anode) with a wire and placing them in contact with an electrolyte, there will also be a voltmeter so that you can measure the voltage of the cell

what is an electrolyte?

a liquid through which ions can flow

what are batteries?

two or more cells connected in series to provide a greater voltage

what three factors affect the voltage of a cell?

1. the metals used for the electrodes - greater difference in reactivity, the greater the voltage will be

2. type and concentration of electrolyte used

3. conditions such as temperature and pH

what makes a good electrolyte

it should be able to conduct electricity and carry ions, so it must be liquid and ideally be an ionic compound to conduct electricity

how does temperature of the electrolyte affect the rate of reaction?

higher temperature increases the rate of collision so in turn increases the rate of reaction

how does the concentration of the electrolyte affect the reaction?

higher concentration increases the likelihood ( rate of collision) as there are more particles per unit of volume so the particles are closer together/less space between the particles so there are a greater number of collisions

what’s the difference between electrolysis and chemical cells?

electrolysis uses electricity to cause a chemical reaction whereas chemical cells use chemical reactions to produce electricity

what are rechargeable cells?

Rechargeable cells are cells and batteries that can be recharged because the chemical reactions are reversed when an external electrical current is supplied

what are some uses of rechargeable cells?

mobile phones and laptops

what are some uses of non rechargeable cells?

alkaline batteries, remote controls, kids toys, smoke alarms

what are non rechargeable cells?

in non rechargeable cells and batteries the chemical reactions stop when one of the reactants has been used up so a voltage is no longer produced, so there is no longer any flow of electrons so the cell stops producing electricity

what are endothermic reactions?

reactions that absorb energy from their surroundings

what are exothermic reactions?

reactions that transfer/release energy to the surroundings usually in the form of heat

what are some examples of an endothermic reaction?

- Photosynthesis

- Melting ice

- Evaporation of water

what are some examples of an exothermic reaction?

- Combustion

- Rusting of iron

- Neutralization reactions

- Respiration

is the reactants higher or lower than the products on a reaction profile for endothermic reactions? Explain a reason for your answer

lower, as energy is absorbed so the products have a higher energy level than the reactants

are the reactants higher or lower than the products on a reaction profile for an exothermic reaction? Explain a reason for your answer

higher, as energy is released to the surroundings so the products have a lower energy level than the reactants

what is activation energy?

the minimum amount of energy the reactant particles need in order to collide with each other and react

the greater the activation energy the _____ energy that will be required to start the reaction

more

how do you find out the overall energy change from a reaction profile?

the line from the reactants to the products

how do you find out activation energy from a reaction profile?

the difference in energy between the top of the curve/hump and the reactant

why do exothermic reactions release energy to the surroundings

because the energy released when forming binds is greater than the energy needed to break bonds

what is a bond energy?

the amount of energy required to break one mole of a particular covalent bond

what is the equation for overall energy change?

energy required to break bonds - energy released forming bonds

what type of reaction is forming bonds and why?

Forming bonds is an exothermic reaction because energy is released when new bonds are created, making the system more stable

what type of reaction is breaking bonds and why?

Breaking bonds is an endothermic reaction, as it requires energy input to overcome the bond energy and break the bonds, it also absorbs heat from the surroundings, making it endothermic.

how do you calculate energy needed to break a bond?

energy needed = moles x bond energy