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Entry Task: May 22 nd 23 rd Block 1 Question: What is temperature change of 50.0 grams of water absorbs 35kJ of energy. (specific heat 4.18 J/gC) You have.

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Presentation on theme: "Entry Task: May 22 nd 23 rd Block 1 Question: What is temperature change of 50.0 grams of water absorbs 35kJ of energy. (specific heat 4.18 J/gC) You have."— Presentation transcript:

1 Entry Task: May 22 nd 23 rd Block 1 Question: What is temperature change of 50.0 grams of water absorbs 35kJ of energy. (specific heat 4.18 J/gC) You have 5 minutes!

2 Agenda: Discuss Ch. 16.sec 2 and worksheet In-class (small notes) on Sec. 3 HW: Look at the specific heats of metal Lab

3 What are endothermic reactions? Endothermic reactions absorb energy (heat) from the surroundings for the reaction to occur.

4 What are exothermic reactions? Exothermic reactions release energy (heat) to the surroundings when the reaction occurs.

5 Define a calorimeter A calorimeter is an insulated device used for measuring the amount to heat absorbed or released during a chemical or physical process.

6 How does it work? A known mass of water is placed in an insulated chamber. The chamber contains the reaction- any heat absorbed in the reaction will drop the temperature of the water. Any heat released in the reaction will raise the temperature of the water.

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8 If 335g of water at 65.5˚C loses 9750 J of heat, what is the final temperature of the water? q= cm ΔT 9750 J = (4.184 J/g˚C)(335g)(X) 9750 (4.184)(335) ˚C is the temperature difference = 58.5 ˚C

9 The temperature of a sample of water increases from 20.0˚C to 46.6˚C as it absorbs 5650 J of heat. What is the mass of the sample? q= cm ΔT 5650 J = (4.184 J/g˚C)(Xg)(26.6˚C) 5650 (4.184)(26.6) = 50.8 g

10 Define thermochemistry Thermochemistry is the study of heat changes that accompany chemical reactions and phase changes

11 Remember this? Order Less energy Less order More energy Chaos Most energy Taking in energy (endothermic) Releases energy (exothermic) Taking in energy (endothermic) Releases energy (exothermic) Releases energy (exothermic) Taking in energy (endothermic)

12 What is the difference between the system, surroundings and universe? The system is the reaction The surroundings is the everything other than the reaction. The universe is the system AND surroundings. System Surroundings UNIVERSE

13 What is the difference between enthalpy and the enthalpy (heat) of reaction? Enthalpy is the heat content in a system at constant pressure. ◦*◦*its almost impossible to know the absolute amount of energy held in a substance. Enthalpy (heat) of reaction is the change of energy- one substance to another. ◦Δ◦Δ H rxn = H final – H initial

14 For an exothermic reaction, heat energy is _____________. When the H reactants is subtracted from the ________H product, a ________ value for ΔH rxn is obtained. Enthalpy changes for exothermic reactions are always_______________. The sign of the enthalpy reactions released smaller negative negative

15 4Fe (s) Provide the enthalpy change reaction for Iron/oxygen reaction +O 2 (g)  2Fe 2 O 3 (s) ΔH= kJ Notice the phase change (s) + (g)  (s) Gas to solid loses energy- exothermic Disorder to order = lose energy

16 For an endothermic reaction, heat energy is _____________. When the H reactants is subtracted from the ________H product, a ________ value for ΔH rxn is obtained. Enthalpy changes for endothermic reactions are always_______________. The sign of the enthalpy reactions absorbed largerpositive positive

17 NH 4 NO 3 (s) Provide the enthalpy change reaction for cold pack with NH 4 NO 3 +NH 4 + (aq)  NO 3 - (aq) ΔH= 27 kJ Notice the phase change (s)  (aq) + (aq) Solid to liquid gains energy - endothermic Order to disorder gains energy

18 Identify the reaction as endothermic or exothermic- PAY ATTENTION TO PHASE CHANGES C 2 H 5 OH (l)  C 2 H 5 OH(g) NH 3 (g)  NH 3 (l) Br 2 (l)  Br 2 (s) NaCl (s)  NaCl (l) C 5 H 12 (g) + 8O 2 (g)  5CO 2 (g) + 6H 2 O(l) Endothermic Exothermic Exothermic Endothermic Exothermic

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20 B C A F D E G

21 8. A scientist is studying the solution in the flask. What is the system? 9. What are the surroundings? 10. What is the universe? The solution The Flask and everything around the flask. Solution + surroundings

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23 NH 4 NO 3 (s) Thermochemical equations +NH 4 + (aq)  NO 3 - (aq) ΔH= 27 kJ Are balanced chemical equations that include physical states of all reactants and products AND the energy change ∆H.

24 Types of enthalpy Change in heat with combustion ∆H (comb) ∆H (vap) ∆H (fus) Change in heat with vaporization Change in heat with fusion

25 H 2 O(l)  H 2 O(g) Thermochemical equations for changes in state Positive- endothermic What is happening? Consider: Its vaporizing. What ∆H would you use? Would it be + or -? ΔH (vap) = 40.7 kJ

26 H 2 O(s)  H 2 O(l) Thermochemical equations for changes in state Positive- endothermic What is happening? Consider: Its melting. What ∆H would you use? Would it be + or -? ΔH (fus) = 6.01 kJ

27 ∆H vap = -∆H cond Pay attention to the signs ∆H fus = -∆H solid H 2 O(g)  H 2 O(l) ΔH (cond) = kJ So -∆H cond for water is So -∆H solid for water is H 2 O(l)  H 2 O(s) ΔH (fus) = kJ Makes sense- both are exothermic -∆H

28 How much heat is released when 54.0 g of glucose (C 6 H 12 O 6 ) is burned? Calculating energy released in a reaction C 6 H 12 O 6 (s) + 6O 2(g)  6CO 2(g) + 6H 2 O (l) ∆H comb = kJ Convert gram to mole ∆H comb = kJ is per mole of glucose 54.0g glucose 180 g glucose 1 mole glucose = 0.3 mol = 0.3 mol X ∆ H comb =842 kJ

29 1. Calculate the heat required to melt 25.7 g of solid methanol at its melting point. You Try!! ∆H (fus) because its melting. So 3.22 its is. Which ∆H would you use? ∆H (fus) be positive or negative? ∆H (fus) be positive. ∆H (fus) = 3.22 per mole.

30 1. Calculate the heat required to melt 25.7 g of solid methanol at its melting point. Convert gram to mole ∆H fus = 3.22 kJ is per mole of methanol 25.7g methanol 32 g methanol 1 mole methanol = mol = mol X 3.22 ∆ H fus = 2.58 kJ

31 2. How much heat is evolved when 275g of ammonia gas condenses to a liquid at its boiling point? ∆H (vap) because its condensing. So 23.3 its is. Which ∆H would you use? ∆H (vap) be positive or negative? ∆H (vap) be negative. ∆H (vap) = per mole.

32 2. How much heat is evolved when 275g of ammonia gas condenses to a liquid at its boiling point? Convert gram to mole ∆H vap = kJ is per mole of ammonia 275g ammonia 17 g a mmonia 1 mole a mmonia = 16.2 mol = 16.2 mol X ∆ H vap = 377 kJ

33 3. What mass of methane must be burned in order to liberate 12880kJ of heat? Methane (CH 4 ) ∆H comb = -891 kJ/mol 14.5 mol methane 16 g m ethane 1 mole m ethane = 232 g ÷ -891 = 14.5 moles of methane

34 2. How much heat is evolved when 275g of ammonia gas condenses to a liquid at its boiling point? Convert gram to mole ∆H vap = kJ is per mole of ammonia 275g ammonia 17 g a mmonia 1 mole a mmonia = 16.2 mol = 16.2 mol X ∆ H vap = 377 kJ

35 Tonight Finish backside w.s AND Pre-lab Questions


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