enthalpy changes in chemistry
Post on 02-Jan-2016
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HeatHeat
• When a chemical reaction takes place heat may be given out or taken in.
1.Exothermic: when heat is given out2.Endothermic: when heat is taken in
Reactants Description of reaction Initial temp. / °C
Final temp. /°C
Change in temp. ΔT / °C
Exo or endo?
Sodium and chlorine gas
https://www.youtube.com/watch?v=Mx5JJWI2aaw
N/A (demo)
N/A (demo)
N/A (demo)
exo
Sugar and sulfuric acid
https://www.youtube.com/watch?v=nqDHwd9rG0s
N/A (demo)
N/A (demo)
N/A (demo)
exo
Dissolving ammonium nitrate
https://www.youtube.com/watch?v=G3S4YvhhAic
N/A (demo)
N/A (demo)
N/A (demo)
endo
Barium hydroxide and ammonium nitrate
https://www.youtube.com/watch?v=GQkJI-Nq3Os
N/A (demo)
N/A (demo)
N/A (demo)
endo
Which of the following statements is correct?
Which of the following statements is correct?
1. The products of a chemical reaction have more energy than the reactants so an exothermic reaction must have taken place.
2. The products of a chemical reaction have less energy than the reactants so an endothermic reaction must have taken place.
3. The products of a chemical reaction have less energy than the reactants so an exothermic reaction must have taken place.
1. The products of a chemical reaction have more energy than the reactants so an exothermic reaction must have taken place.
2. The products of a chemical reaction have less energy than the reactants so an endothermic reaction must have taken place.
3. The products of a chemical reaction have less energy than the reactants so an exothermic reaction must have taken place.
Which of the following statements is correct?
Which of the following statements is correct?
3 is correct!The products of a chemical reaction have less energy than the reactants so an exothermic reaction must have taken place.
Q - How can we illustrate this?
Energy level diagrams – copy into your notes
Energy level diagrams – copy into your notes
Endothermic Exothermic
Heat taken inHeat taken in Heat given outHeat given out
Energy level of products is higher than reactants so heat taken in.Energy level of products is higher than reactants so heat taken in.
Energy level of products is lower than reactants so heat given out.Energy level of products is lower than reactants so heat given out.
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