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Thermochemical equations A typical chemical equation is S + O 2 SO 2 It is called a thermochemical equation when we add information about H … S + O 2 SO.

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Presentation on theme: "Thermochemical equations A typical chemical equation is S + O 2 SO 2 It is called a thermochemical equation when we add information about H … S + O 2 SO."— Presentation transcript:

1 Thermochemical equations A typical chemical equation is S + O 2 SO 2 It is called a thermochemical equation when we add information about H … S + O 2 SO 2 H = – kJ If we change the equation, then the H also changes … SO 2 S + O 2 H = kJ If the reaction is reversed the sign is reversed Also, if numbers in the equation change, so will the amount of energy produced/absorbed: 2S + 2O 2 2SO 2 H = – kJ Read 1st part of handout. Do Q 1-3

2 Answers C + O 2 CO kJ Q2H 2 + I 2 2HI H = kJ Q1C + O 2 CO 2 H = – kJ Q31/2H 2 + 1/2I 2 HI H = kJ 2HI 53.2 kJ H 2 + I 2

3 Answers pg. 175, Q At STP (25°C and 1 atm) The H° value Moles. (You cant have 1/2 an atom) answer in back of book 4Al(s) + Fe 2 O 3 (s) 2Al 2 O 3 (s) + 4Fe(s) H° = kJ

4 Answers pg. 175, Q If 2 = 6542 kJ then 1.5 = 4907 kJ (6542/2 x 1.5) Actually, it should be kJ since it is exothermic CaO(s) + 10H 2 O(l) 10Ca(OH) 2 (s) H° = -653 kJ Equation is reversed, thus H° sign changes Equation is multiplied by 10, thus so is H°

5 Standard heats of reaction 5.45° indicates 1 atm (and is usually associated with a temperature of 25°C) 5.46An energy term is added (e.g. H or H°) 5.47 Moles 5.48 Al(s) + 1/2Fe 2 O 3 (s) Fe(s) + 1/2Al 2 O 3 (s) H ° = – kJ 4Al(s) + 2Fe 2 O 3 (s) 4Fe(s) + 2Al 2 O 3 (s) H ° = – 1708 kJ is 3/4 of 2. 3/4 of 6542 kJ is kJ CaO(s) + 10H 2 O(l) 10Ca(OH) 2 (s) H ° =–653kJ For more lessons, visit


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