S3 Energy Changes Flashcards
What are the 3 characteristics that define an exothermic reaction?
1) experimental set up loses heat to surroundings
2) after the reaction, products has less energy than the reactants
3) negative Delta H
What are 5 examples of an exothermic reaction?
1) combustion
2) oxidation of metals (rusting of iron)
3) dissolving acids and alkali in water
4) neutralisation
5) nuclear reactions
What are 3 characteristics that define an endothermic reaction?
1) experimental setup gains heat from surrounding
2) after reaction, the products has more energy than reactants
3) positive Delta H
What are 4 examples of endothermic reactions?
1) photosynthesis
2) photography (heat on AgBr)
3) dissolving of some ionic compounds (ammonium chloride, potassium nitrate, copper(II) sulfate)
4) thermal decomposition
What is enthalpy change?
It is the amount of heat energy given out or absorbed during a chemical reaction.
What happens between the reactants of a reaction?
1) bonds are broken
2) energy is absorbed (endothermic)
What happens between products of a reaction?
1) bonds are formed
2) energy is given out (exothermic)
What are fossil fuels?
Carbon compounds formed from decayed plants and animals that lived millions of years ago.
What are 3 examples of fossil fuels?
1) coal
2) petroleum (CH4)
3) natural gas
Explain in terms of bond breaking and bond forming, why the overall reaction is exothermic.
Energy absorbed during breaking of bonds in reactants is less than energy released during forming of bonds in products. Thus, the enthalpy change for overall reaction is exothermic.
Explain in terms of bond breaking and bond forming, why the overall reaction is endothermic.
Energy absorbed during breaking of bonds in reactants is more than energy released during forming of bonds in products. Thus, the enthalpy change for overall reaction is endothermic
Explain in terms of bond breaking and bond forming, why the overall reaction is exothermic.
Energy absorbed during breaking of bonds in reactants is less than energy released during forming of bonds in products. Thus, the enthalpy change for overall reaction is exothermic.
Explain in terms of bond breaking and bond forming, why the overall reaction is endothermic.
Energy absorbed during breaking of bonds in reactants is more than energy released during forming of bonds in products. Thus, the enthalpy change for overall reaction is endothermic
What are fuels?
Substances that burn easily in air to give out energy.
Why is hydrogen used as alternative fuel?
When hydrogen burns, the product is steam which does not pollute the air.
