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Chem10 Topic 01 - Thermochemistry

Chem10 Topic 01 - Thermochemistry. Science 10 CT01D04. Stoichi what?. Stoikheion ( greek )= element Metron ( greek )= to measure Stoichiometry: the calculation of amounts of substances involved in chemical reactions This will be Topic 01 in IB Chemistry. Moles.

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Chem10 Topic 01 - Thermochemistry

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  1. Chem10 Topic 01 - Thermochemistry Science 10 CT01D04

  2. Stoichi what? • Stoikheion (greek)= element • Metron (greek)= to measure • Stoichiometry: the calculation of amounts of substances involved in chemical reactions • This will be Topic 01 in IB Chemistry

  3. Moles • Moles (latin): heap or pile • 1 Mole (mol) = 6.02 x 1023 representative particles (atoms or molecules) • This is called Avogadro’s number

  4. A Mole Never Changes!

  5. Molar Mass • The atomic mass of one mole of an element or molecule expressed in grams • Round to 2 decimal places, your periodic table should already have this!

  6. Some Molar Masses of Elements

  7. Calculating Molar Mass • Step One: Find the molar mass (atomic mass) of each element on the PT • round to 2 decimal places • Unit is grams (g) per mole (mol) • Step Two: Multiply the number of atoms of the element by the molar mass • Remember – the subscript tells you how many atoms you have of each element • Step Three: Add up the masses of all elements in the compound

  8. Example

  9. Some Molar Masses of Molecules

  10. Units for Molar Mass • H2O is 18.02 g/mol • Stated as “grams per mol” • Meaning 18.02 grams = 1 mole • OR 1 mole = 18.02 grams • Use like common conversions • How many meters in 1.000 km? • Use the conversion of 1000 m = 1.000 km

  11. Moles to Volume (Molar Volume of a gas 22.4) Moles to Molecules (use Avogadro’s Number) Moles to Mass (use Molar Mass)

  12. Simple Conversions: - Mole / Mass Conversions - Use the Molar Mass of a substance to convert from Moles to Mass and Mass to Moles 80. g CuSO4 1 mol CuSO4 Mass to Moles  = 0.50 mol CuSO4 159.5 g CuSO4 0.50 mol CuSO4 159.5 g CuSO4 Moles to Mass  = 80. g CuSO4 1 mol CuSO4

  13. Simple Conversions: - Mole / Molecule Conversions - Use Avogadro’s Number : 6.022 x 1023 molecules (mc) in one mole of the substance 2 mol CuSO4 6.022x1023 (mc) CuSO4 Moles to (mc)  = 1.2x1024 (mc) CuSO4 1 mol CuSO4 1.2x1024 (mc) CuSO4 1 mol CuSO4 (mc) to Moles  = 2 mol CuSO4 6.022x1023 (mc) CuSO4

  14. Let’s use it, but first… • You needed to calculate q (heat change) for NaOHand Na2S2O3. Lets use NaOH as our example: • qNaOH cannot be found directly, but qH2O can be • qNaOH = - (qH2O) (this is the conservation of energy) • qH2O = msΔT • m = 50.00 g • s = 4.184 J/goc • ΔT =20.00 oc • qH2O = (50.00 g)(4.184 J/goc)(20.00oc) • qH2O = 4,184 J • qNaOH = -4,184 J • Now, how many grams of NaOH were used to produce this amount of heat? (for my data it was 1.24 g NaOH) First Law of Thermodynamics! Energy lost = Energy gained q = -q

  15. Calculate Molar Heat of Solution • For a 7 on the Heat Change Lab you were asked to calculate the molar heat change • In my reaction example, with 1.24 g NaOHI produced a value of qNaOH= -4,184 J • So, lets write this in units of Joules per gram • qNaOH = • You need to find Joules per mole (molar heats of solution) so that you can relate to the heat production of the other salt. • NaOH(s)  Na+(aq) + OH-(aq) qNaOH = -134 kJ/mol • Na2S2O3(s)  2 Na+(aq) + S2O32-(aq) qNa2S2O3 = + or - ??

  16. Enthalpy: Thermochemical Equations NaOH(s) Is DH negative or positive? System gives off heat Exothermic DH < 0 Na+(aq) + OH-(aq) 134 kJ are released for every 1 mole of sodium hydroxide that is dissolved into water. • NaOH(s)  Na+(aq) + OH-(aq) qNaOH= -134 kJ/mol • ΔH = -134 kJ/mol

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