Chemistry topic 5

What’s is an endothermic reaction

A reaction that transfers energy to the surroundings which cause the temperature in the surroundings increases

What is an endothermic reaction

A reaction that takes in energy from the surroundings which cause the temperature of the surroundings to decrease f

What is a profile diagram

A diagram that shows the energy change during a chemical

What are the three things to focus on in a profile diagram

Reactants

Activation enegy

Products

Examples of exothermic reactions

Combustion

Neutralisation

Oxidation

Examples of endothermic reactions

Thermal decomposition

Citric acid + sodium hydrogen carbonate

What does it mean when the reactants are more than the products

The reaction is exothermic d

Calculating the energy change of a reaction formula

(Energy Required to break bonds) - (energy released by forming bonds)

What type of reaction is it when the energy change is negative

Exothermic (positive is endothermic)

What is an electrochemical cell

A device that generates electrical energy from the chemical reactions happening in it

Formed from 2 electrodes in contact with each other

How is an electrochemical cell set up

Electrodes: 2 different metals conducting electricity

Voltmeter: connected to electrodes with wire

Electrolyte - solution that contains ions that react with electrodes

What affect the voltage of an electrochemical cell

the reactivity of the electrolyte and electrodes affect the voltage of a cell

Why do non-rechargeable batteries run out

The chemical reactants are fully used up

How are rechargeable batteries recharged

The chemical reactions are reversed when an external current is supplied

Are alkaline batteries rechargeable

No

What is a fuel cell

An electrical cell supplied with fuel and oxygen that uses energy from the reaction to produce electricity

Advantages of fuels cells in cars

Don’t produce pollutants

Rechargeable

Fuels cells store more energy than batteries

Disadvantages of fuel cells in cars

Hydrogen takes up lots of space since it’s a gas

Hydrogen is explosive

Making hydrogen requires electricity

Overall reactions in a hydrogen m- oxygen fuel cell

2H2 + O2 → 2H2O

What’s the common use for an electrolyte in hydrogen fuels cells

Phosphoric acid

What’s the reaction at the anode in hydrogen oxygen fuel cells

H2 → 2e- + 2H+

What’s the reaction at the cathode in the hydrogen-oxygen fuel cell

4H+ + O2 + 4e- → 2H2O

How do hydrogen oxygen fuels cells work

Hydrogen goes to the negative anode and oxygen in the positive cathode

Hydrogen loses electrons and form H+ ions and these ions move to the cathode

Oxygen gains electrons at the cathode and then reacts with H+ ions to make water

The overall reaction is hydrogen + oxygen makes water

What are the electrodes in fuel cells made from

Porous carbon