TOPIC 5 - Energy

If a student different make any measuring errors, what could cause random errors in a temperature change experiment?

the starting temperatures may be different; inconsistent stirring

In a chemical cell, by measuring the voltage, how can you order the metals from most to least reactive?

the higher the (positive) voltage, the more reactive the metal

Plan an experiment to investigate how the voltage produced by a chemical cell varies with the concentration of the electrolyte solution (have a 1.0mol/dm3 salt solution, pure water, metal electrodes)

• set up cell with sodium chloride sol as electrolyter
• use two diff metals as electrodes
• measure the voltage
• repeat at different cons of electrolyte solution
• by diluting the sodium chloride solution with water 
• using measure volumes of sodium chloride sol and water
• measure volume with measuring cylinder 
• use the same two metals each time
• use same volume of electrolyte solution

How does a Hydrogen fuel cell produce a potential difference?

hydrogen is oxidised (electrochemically); to produce water

What does H2O(g) mean?

water vapour

Which two variables should the student keep the same to make this a fair test?

starting temperature of HCl acid; volume of HCl acid

What to use instead of a glass cup?

A polystrene cup with a lid to prevent energy transfer

How could  you improve using just a thermometer?

use a digital thermometer - easier to read

Why should batteries not be put in household waste bins?

• the metal/ alkaline waste can be toxic/ corrosive
• The waste could cause pollution in landfill sites
• recycling them would save resources

Factors that could affect the voltage produced

• the type of electrode
• type of electrolyte
• the temperature of the electrolyte/ solution
• concentration of electrolyte
• the mass/ length/ SA of the electrode

What are two variables the student should keep the same to make the investigation valid in chemical cells?

the concentration of electrolyte; the temperature of the electrolyte

Describe how to make a 12 V battery using 1.5 V cells

connect 8 cells in series

Disadvantages of hydrogen fuel cells

• hydrogen is made from fossil fuels/ non-renewable resources
• hydrogen is explosive
• hydrogen is difficult to store
• costs more to refuel (than to recharge a battery)
• not many hydrogen filling stations

Why do alkaline batteries eventually stop working?

a reactant is used up so the reaction stops

Why can alkaline batteries not be recharged?

the reaction is not reversible

Hydrogen fuel cells vs Rechargable batteris

• time to refuel is faster than recharging
• a fuel cell has a greater range than R
• H can be renewable if from electrolysis w/ renewable energy
• But H often from fossil fuels so not renewable
• Lithium-ion Rbs can catch fire
• Hfcs produce only water, no pollutants
• R may release toxic chemicals on disposal
• R can't be recharged forever, eventually can't -> finite life
• Li-I uses energy more efficiently
• Cost of R car much less
• Cost of recharging is much less than refuelling
• Charging points are move widely available than filling stations
• Hydrogen takes up a lot of space; difficult to store; highly flammable
• No emmision from R batteries

Why are Hydrogen-fuel cells seen as non-polluting?

only produces water; water isn't polluting; doesn't produce carbon dioxide

Why can a rechargeable cell be recharged?

the chemical reaction is reversible

From a table, which metal is the least reactive?

copper; gave the most negative voltages when it was metal 2/ gave biggest voltage with chromium

Write the two half equations for the reactions that occur at the electrodes in a hydrogen fuel cell

H2 -> 2H+ + 2e-
O2 + 4H+ + 4e- --> 2H2O