Day 5 N otes Unit Thermochemistry Heating Curves

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Day 5 -N otes Unit: Thermochemistry Heating Curves

Day 5 -N otes Unit: Thermochemistry Heating Curves

After today you will be able to… • Explain what occurs on each point

After today you will be able to… • Explain what occurs on each point of a heating curve • Calculate the total energy required for water to go through phase changes

Heating Curves A heating curve is a graph of temperature versus time. • It

Heating Curves A heating curve is a graph of temperature versus time. • It describes the enthalpy changes that take place during phase changes.

Heating Curves When a solid substance is heated, its temperature will increase until it

Heating Curves When a solid substance is heated, its temperature will increase until it reaches its melting point (m. p. ). • Temperature will then stay constant during the melting process.

Heating Curves When a substance is completely melted, its temperature will again increase until

Heating Curves When a substance is completely melted, its temperature will again increase until it has reached its boiling point (b. p. ). • Temperature stays constant during boiling. • Once completely vaporized, the temperature will again increase.

Heating curve problems involve TWO types of calculations: 1. q=mcΔT, use for temperature changes

Heating curve problems involve TWO types of calculations: 1. q=mcΔT, use for temperature changes 2. Dimensional analysis using the ΔH, where there is a phase change (flat line), mass will be the “known. ”

The type of phase change will determine the ΔH to be used: • Molar

The type of phase change will determine the ΔH to be used: • Molar heat of fusion (ΔHfus): the amount of energy required to melt a substance (solid liquid) • Molar heat of vaporization (ΔHvap): the amount of energy required to vaporize (boil) a substance (liquid gas)

BOILING (ΔHvap) Temp (˚C) MELTING (ΔHfus) -5. 00˚C q= ICE m cΔ T 0˚C

BOILING (ΔHvap) Temp (˚C) MELTING (ΔHfus) -5. 00˚C q= ICE m cΔ T 0˚C LIQ q= UI mc D ΔT 100˚C Time q= GA m S cΔ T Example: What is the total amount of heat in Joules (J) that must be added to 165 g of ice (solid H 2 O) at -5. 00°C to change it into steam at 103°C? ΔHfus= +6. 01 k. J/mol ΔHvap= +40. 7 k. J/mol cice= 2. 01 J/g°C cwater= you know this already! csteam= 2. 02 J/g°C

Example: What is the total amount of heat in Joules (J) that must be

Example: What is the total amount of heat in Joules (J) that must be added to 165 g of ice (solid H 2 O) at -5. 00°C to change it into steam at 103°C? s as s! m e ig Us sig f for ΔHfus= +6. 01 k. J/mol ΔHvap= +40. 7 k. J/mol cice= 2. 01 J/g°C cwater= you know this already! csteam= 2. 02 J/g°C 100˚C (4) Temp (˚C) 0˚C (5) (3) (2) (1) -5. 0˚C (1) Ice, q=mcΔT q=(165 g)(2. 01 J/g˚C)(5. 00˚C) q=+1660 J (2) Melting, ΔHfus, DA calc Time (4) Boiling, ΔHvap DA calc 165 g. H 2 O x 1 mol H 2 O x +40. 7 k. J x 1000 J = +373, 000 J 18. 02 g. H 2 O 1 mol H 2 O 1 k. J 165 g. H 2 O x 1 mol H 2 O x +6. 01 k. J x 1000 J = +5. 50 x 104 J 18. 02 g. H 2 O 1 mol H 2 O 1 k. J (3) Liquid, q=mcΔT q=(165 g)(4. 18 J/g˚C)(100˚C) (5) Gas, q=mcΔT q=(165 g)(2. 02 J/g˚C)(3˚C) q=+6. 90 x 104 J q=+1. 00 x 103 J TOTAL ENERGY (J): +499, 660 J

Questions? Complete WS 5

Questions? Complete WS 5