Water and Energy Changes Flashcards
What is filtration?
Water is sprayed onto layers of sand and gravel and as it trickles through, insoluble molecules are removed
What is sedimentation?
A chemical is added to cause tiny solid particles to clump together
What is chlorination and why is it good and bad?
Chlorine gas is injected into water. It kills harmful microbes but can react with harmless organic molecules to form toxic products like THM
What is good and bad about adding fluorine to water?
It prevents tooth decay, but it causes learning difficulties and Alzheimers in the elderly
What causes water hardness in temporary and permanent hard water?
Temporary - calcium and magnesium hydrogencarbonate
Permanent - calcium and magnesium sulphate, nitrate or chloride
Why does reacting hard water with soap from scum?
sodium stearate+calcium ions__calcium stearate+precipitate(scum)+sodium ions
When can soap lather?
When all calcium and magnesium ions have reacted
Advantages of hard water?
- Good for bone development
- Tastes better
- Reduces heart disease
Disadvantages of hard water?
- Forms scum with soap
- Temporary forms scale when boiled
How can temporary hardness be removed?
Boiling the water, decomposing hydrogencarbonate ions to carbonate ions that react with ca/mg ions to form limescale. This removes the ca/mg ions from the water
How can permanent hardness be removed?
- Adding sodium carbonate. This leaves soluble sodium ions and ca/mg carbonate that can be filtered out.
- Ion exchange column. Contains resins that replace ca/mg ions with sodium/hydrogen ions.
How can resins be recharged with sodium ions?
Washing them with salt solution
Why do water filters contain carbon and nanoparticles of silver?
To absorb impurities and kill microbes
How is sea water desalinated?
Boiled and turned to steam, leaving salt behind, and then condensed to water.
Advantages of softening water?
- Do not waste soap
- Do not get scum
- Do not get scale when heating water
- Better for industrial processes like dyeing
Disadvantages of softening water?
- Expensive
- Hard water tastes better
- Sodium ions give high blood pressure
How do you measure the energy released by burning a food or fuel?
Heat is captured by water and temperature rise calculated.
What equation do you use to calculate the energy released by a food or fuel?
mass of water(g) X 4.2 X change in water temperature
How do you convert calories to joules?
X 4.2
Exothermic reaction?
More energy is released when new bonds are made than needed to break old bonds. The spare energy is released as heat.
Endothermic reaction?
More energy is needed to break old bonds than is released when new bonds are made. The extra energy is taken from the surroundings.
How do you calculate an energy change?
Add up number of each type of bond, multiply by bond energies and add answers together for reactants. Repeat for products. Reactants-products=energy change. If the answer is negative, the reaction is exothermic.
Why is incomplete combustion less exothermic than complete?
It releases less energy
How do you calculate a heat change of a fuel (kJ/mole)
1) mXcXt - convert to kJ
2) calculate mass of fuel used in reaction
3) calculate amount of fuel in moles
4) step1 / step3
