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Endothermic & Exothermic Reactions

Endothermic & Exothermic Reactions. Enthalpy - ( H) Heat Enthalpy Change - ( Δ H) The change in heat for a reaction. Endothermic reactions Energy is absorbed Heat goes into the system from the surroundings the surroundings will feel colder Temperature of surroundings goes down + Δ H

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Endothermic & Exothermic Reactions

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  1. Endothermic & Exothermic Reactions • Enthalpy- (H) Heat • Enthalpy Change- (ΔH) The change in heat for a reaction

  2. Endothermic reactions • Energy is absorbed • Heat goes into the system from the surroundings • the surroundings will feel colder • Temperature of surroundings goes down • +ΔH • Exothermic reactions • energy is released • Heat goes out of the system into the surroundings • Temperature of the surrounding will increase • -∆H

  3. Surroundings System Heat Endo- and Exothermic Surroundings System Heat ENDOTHERMIC EXOTHERMIC

  4. Endothermic & Exothermic Reactions

  5. Endothermic & Exothermic Reactions

  6. Endothermic & Exothermic Reactions • Are the following reactions endothermic or exothermic? • CO + 3H2 CH4 + H2O H= -206kJ • Exothermic (H is negative) • I add magnesium metal to some hydrochloric acid. The temperature goes from 23C to 27 C • Exothermic – temperature goes up • I mix together some vinegar & baking soda. The temperature goes from 28C to 23C • Endothermic – temperature goes down

  7. Thermochemical equations • An equation that gives us information about H … S + O2 SO2H = – 296.9 kJ • If we change the equation, then the H also changes … SO2 S + O2H = + 296.9 kJ • If the reaction is reversed the sign is reversed • Also, if the coefficients in the equation change, so will the amount of energy produced/absorbed: 2S + 2O2 2SO2H = – 593.8 kJ

  8. Given the following thermochemical equation: • CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l) ΔH = -890.4 kJ/mol • calculate the heat evolved when 20.00 g of CH4reacts • The chemical equations are always written in terms of moles, but the problem is stated in terms of mass (g). • First, convert grams to moles. • Then, convert moles to kJ (kilojoules)

  9. CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l) ΔH = -890.4 kJ/mol • 20.00g CH4 1 mole CH4 -890.4 kJ 16.04g CH4 1 mole CH4 (from the coefficient in the equation) • -1110. kJ

  10. CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O (l)∆H = - 890.4 kJ • How much energy is given off when 2.00 mol of CH4 are burned? • How much energy is released when 22.4g of CH4 are burned? • If you were to attempt to make 45.0g of methane from CO2 and H2O , how much energy would be required?

  11. -1780 kJ • -1240 kJ • 2.50 x 103 kJ

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