1 / 21

Thermochemistry

Thermochemistry . DO NOW. The specific heat of ethanol is 2.44 J/ g°C . How many kilojoules of energy are required to heat 50.0 g of ethanol from -20.0°C to 68°C?. Objective . Describe how calorimeters are used to measure heat flow . Construct thermochemical equations .

luisa
Télécharger la présentation

Thermochemistry

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Thermochemistry

  2. DO NOW • The specific heat of ethanol is 2.44 J/g°C. How many kilojoules of energy are required to heat 50.0 g of ethanol from -20.0°C to 68°C?

  3. Objective • Describe how calorimeters are used to measure heat flow. • Constructthermochemical equations. • Solve for enthalpy changes in chemical reactions by using heats of reaction.

  4. Calorimetry • Calorimetry - the measurement of the heat into or out of a system for chemical and physical processes. • Based on the fact that the heat released = the heat absorbed • The device used to measure the absorption or release of heat in chemical or physical processes is called a “Calorimeter”

  5. Enthalpy • Heat absorbed or released by a reaction at constant pressure H = qq = H = m x C x T Note: We cannot calculate the actual value of enthalpy, only the change in enthalpy

  6. Thermochemical equation • Includes the ΔH as either a product or a reactant CaO(s) + H2O(l)  Ca(OH)2(s) + 65.2 kJ

  7. Heat of Reaction H = Hproducts – Hreactants

  8. Exothermic Reaction 2CO(g) + O2(g)  2CO2(g) H = -566.8 kJ Or 2CO(g) + O2(g)  2CO2(g) + 566.8 kJ Negative sign means energy is released

  9. Energy Change is down ΔH is <0 = Exothermic (heat is given off) Reactants ® Products

  10. 2CO + O2 Energy 2CO2 Reactants ® Products 2CO(g) + O2(g) → 2CO2(g) + 566.8 kJ 566.8kJ given off

  11. Endothermic Reaction 2CO2(g)  2CO(g) + O2(g) H = +566.8 kJ Or 2CO2(g) + 566.8 kJ  2CO(g) + O2(g) Positive sign means energy is absorbed

  12. Energy Change is up ΔH is > 0 = Endothermic (heat is absorbed) Reactants ® Products

  13. 2CO(g) + O2(g) Energy 2CO2(g) Reactants ® Products CaCO3→ CaO + CO2 2CO2(g) + 566.8 kJ →2CO(g) + O2(g) 566.8kJ absorbed

  14. Chemistry Happens in MOLES • An equation that includes energy is called a thermochemical equation • CH4 + 2O2® CO2 + 2H2O + 802.2 kJ • 1 mole of CH4 releases 802.2 kJ of energy. • When you make 802.2 kJ you also make 2 moles of water

  15. The magnitude of ΔH is directly proportional to the amount of reactants or products. • 1A + 2 B ----> 1C ΔH = -100 kJ • 1/2 A + 1B ----> 1/2 C ΔH = -50 kJ

  16. CH4 + 2O2® CO2 + 2H2O; ΔH = -802.2 kJ Rewrite chemical equation as a thermochemical equation. Exothermic or endothermic reaction? If 3 moles of O2 react with excess CH4 how much heat will be produced?

  17. 1CH4(g) + 2 O2(g)® CO2(g) + 2 H2O(l) + 802.2 kJ • If 10. 3 grams of CH4 are burned completely, how much heat will be produced? Convert moles to desired unit Convert to moles Start with known value 1 mol CH4 802.2 kJ 10. 3 g CH4 16.05 g CH4 1 mol CH4 = 514 kJ Ratio from balanced equation ΔH = -514 kJ, which means the heat is released for the reaction of 10.3 grams CH4

  18. 4 NO(g) + 6 H2O(l)  4 NH3(g) + 5 O2(g)    ΔH = +1170 kJ • Based upon the thermochemical equation given, calculate the heat associated with the decomposition of 1.15 g of NO.

  19. 2 C2H6(g) + 7 O2(g)  4 CO2(g) + 6 H2O(l)   ΔH = -3120 kJ • Calculate the mass of ethane, C2H6, which must be burned to produce 100 kJ of heat.

  20. Heat of Reaction CaO(s) + H2O(l)  Ca(OH)2(s) ΔH = -65.2 kJ CaO + H2O Enthalpy (H) ΔH = -65.2 kJ Ca(OH)2

More Related