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Chapter 17: Cells and Batteries

17.1-Bond Energies

Energy must always be supplied to break bonds

  • During a chemical reaction, old bonds are broken and new bonds are formed

  • Energy must be supplied to break existing bonds, so bond breaking is an endothermic process

  • Energy is released when new bonds are formed, so bond formation is an exothermic process

  • In exothermic reactions the energy released by forming bonds is greater than the energy to break them

  • In endothermic reactions the energy used to break bonds is greater than the energy released by forming them

Bond energy calculations-need to be practised

  • Every chemical bond has a particular bond energy associated with it

  • This bond energy varies slightly depending on the compound the bond occurs in

  • You can use these known bond energies to calculate the overall energy changes for a reaction

  • The overall energy change is the sum of the energies needed to break bonds in the reactants minus the energy released when the new bonds are formed in the products

  • You can’t compare the overall energy changes of reactions unless you know the numerical differences in the bond energies

17.2-Cells and Batteries

Simple Cells

  • A simple cell is a source of electrical energy

  • The simplest design consists of two electrodes made from metals of different reactivity immersed in an electrolyte and connected to an external voltmeter by wire, creating a complete circuit

  • A common example is zinc and copper

  • Zinc is the more reactive metal and forms ions more easily, readily releasing electrons

  • The electrons give the more reactive electrode a negative charge and sets up a charge difference between the electrodes

  • The electrons then flow around the circuit to the copper electrode which is now the more positive electrode

  • The difference in the ability of the electrodes to release electrons causes a voltage to be produced

  • The greater the difference in the metals reactivity then the greater the voltage produced

    • Voltage = an electromotive force or potential difference expressed in volts.

  • The electrolyte used also affects the voltage as different ions react with the electrodes in different ways

17.3-Fuel Cells

What are fuel cells?

  • Chemical cells use chemical reactions to convert and transfer energy to electrical energy.

  • They will produce a voltage only up until one of the reactants has been used up (we say the battery has "gone flat").

  • Fuel cells will produce a voltage continuously, provided they have a constant supply of fuel and oxygen (from the air).

Hydrogen-oxygen fuel cells

  • In this type of fuel cell, hydrogen and oxygen are used to produce a voltage.

  • The only product from this reaction is water.

  • A hydrogen-oxygen fuel cell and electric motor are much quieter, and need less maintenance, than a petrol or diesel engine, but the hydrogen still needs to be stored in a container - like a tank.

Uses of Fuel Cells

  • Hydrogen, diesel and petrol are all highly flammable fuels. Fuel cells have their advantages and disadvantages depending on the use.

Fuel cells in spacecraft

Strengths

Weaknesses

No moving parts to maintain

Have to be continuously supplied with oxygen and hydrogen

Small in size for the amount of electricity produced

Water they produce can be used for drinking water

Fuel cells in vehicles

Strengths

Weaknesses

fuel cells

Fewer moving parts

Hydrogen is difficult to store since there aren't many places to fill up with hydrogen fuel

petrol/diesel

Easier to store so easier distribution

Noisy during useCarbon dioxide is a waste product

Practice Questions:

  • How do cells produce electricity?

    • Cells contain chemicals in the form of a solid metal (electrode) and an ionic solution (the electrolyte), which react and generate electricity by releasing electrons. The voltage produced by a cell depends on the type of electrode and electrolyte used.

  • Weakness of fuel cells

    • Hydrogen is difficult to store

  • What are fuel cells?

    • Chemical cells use chemical reactions to convert and transfer energy to electrical energy.

  • What are simple cells?

    • A source of electrical energy

Chapter 17: Cells and Batteries

17.1-Bond Energies

Energy must always be supplied to break bonds

  • During a chemical reaction, old bonds are broken and new bonds are formed

  • Energy must be supplied to break existing bonds, so bond breaking is an endothermic process

  • Energy is released when new bonds are formed, so bond formation is an exothermic process

  • In exothermic reactions the energy released by forming bonds is greater than the energy to break them

  • In endothermic reactions the energy used to break bonds is greater than the energy released by forming them

Bond energy calculations-need to be practised

  • Every chemical bond has a particular bond energy associated with it

  • This bond energy varies slightly depending on the compound the bond occurs in

  • You can use these known bond energies to calculate the overall energy changes for a reaction

  • The overall energy change is the sum of the energies needed to break bonds in the reactants minus the energy released when the new bonds are formed in the products

  • You can’t compare the overall energy changes of reactions unless you know the numerical differences in the bond energies

17.2-Cells and Batteries

Simple Cells

  • A simple cell is a source of electrical energy

  • The simplest design consists of two electrodes made from metals of different reactivity immersed in an electrolyte and connected to an external voltmeter by wire, creating a complete circuit

  • A common example is zinc and copper

  • Zinc is the more reactive metal and forms ions more easily, readily releasing electrons

  • The electrons give the more reactive electrode a negative charge and sets up a charge difference between the electrodes

  • The electrons then flow around the circuit to the copper electrode which is now the more positive electrode

  • The difference in the ability of the electrodes to release electrons causes a voltage to be produced

  • The greater the difference in the metals reactivity then the greater the voltage produced

    • Voltage = an electromotive force or potential difference expressed in volts.

  • The electrolyte used also affects the voltage as different ions react with the electrodes in different ways

17.3-Fuel Cells

What are fuel cells?

  • Chemical cells use chemical reactions to convert and transfer energy to electrical energy.

  • They will produce a voltage only up until one of the reactants has been used up (we say the battery has "gone flat").

  • Fuel cells will produce a voltage continuously, provided they have a constant supply of fuel and oxygen (from the air).

Hydrogen-oxygen fuel cells

  • In this type of fuel cell, hydrogen and oxygen are used to produce a voltage.

  • The only product from this reaction is water.

  • A hydrogen-oxygen fuel cell and electric motor are much quieter, and need less maintenance, than a petrol or diesel engine, but the hydrogen still needs to be stored in a container - like a tank.

Uses of Fuel Cells

  • Hydrogen, diesel and petrol are all highly flammable fuels. Fuel cells have their advantages and disadvantages depending on the use.

Fuel cells in spacecraft

Strengths

Weaknesses

No moving parts to maintain

Have to be continuously supplied with oxygen and hydrogen

Small in size for the amount of electricity produced

Water they produce can be used for drinking water

Fuel cells in vehicles

Strengths

Weaknesses

fuel cells

Fewer moving parts

Hydrogen is difficult to store since there aren't many places to fill up with hydrogen fuel

petrol/diesel

Easier to store so easier distribution

Noisy during useCarbon dioxide is a waste product

Practice Questions:

  • How do cells produce electricity?

    • Cells contain chemicals in the form of a solid metal (electrode) and an ionic solution (the electrolyte), which react and generate electricity by releasing electrons. The voltage produced by a cell depends on the type of electrode and electrolyte used.

  • Weakness of fuel cells

    • Hydrogen is difficult to store

  • What are fuel cells?

    • Chemical cells use chemical reactions to convert and transfer energy to electrical energy.

  • What are simple cells?

    • A source of electrical energy