Presentation on theme: "Entry Task: May 22nd 23rd Block 1"— Presentation transcript:
1 Entry Task: May 22nd 23rd 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. 3HW: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.What are endothermic reactions?
4 What are exothermic reactions? Exothermic reactions release energy (heat) to the surroundings when the reaction occurs.What are exothermic reactions?
5 A calorimeter is an insulated device used for measuring the amount to heat absorbed or released during a chemical or physical process.Define a calorimeter
6 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.How does it work?
8 q= cmΔT9750 J = (4.184 J/g˚C)(335g)(X)9750(4.184)(335)6.96 ˚C is the temperature difference= ˚CIf 335g of water at 65.5˚C loses 9750 J of heat, what is the final temperature of the water?
9 q= cmΔT5650 J = (4.184 J/g˚C)(Xg)(26.6˚C)5650(4.184)(26.6)111.29= 50.8 gThe 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?
10 Define thermochemistry Thermochemistry is the study of heat changes that accompany chemical reactions and phase changesDefine thermochemistry
11 Remember this? Chaos Most energy Taking in energy (endothermic) Releases energy(exothermic)Taking in energy(endothermic)Releases energy(exothermic)Taking in energy(endothermic)OrderLess energyLess orderMore energyReleases energy(exothermic)
12 What is the difference between the system, surroundings and universe? The system is the reactionThe surroundings is the everything other than the reaction.The universe is the system AND surroundings.SurroundingsUNIVERSESystemWhat is the difference between the system, surroundings and universe?
13 ΔHrxn = Hfinal – Hinitial 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.ΔHrxn = Hfinal – HinitialWhat is the difference between enthalpy and the enthalpy (heat) of reaction?
14 The sign of the enthalpy reactions For an exothermic reaction, heat energy is _____________.When the Hreactants is subtracted from the ________Hproduct, a ________ value for ΔHrxn is obtained.Enthalpy changes for exothermic reactions are always_______________.releasedsmallernegativenegative
15 Notice the phase change Provide the enthalpy change reaction for Iron/oxygen reaction4Fe (s)+O2 (g)2Fe2O3 (s)ΔH= kJNotice the phase change(s) + (g) (s)Gas to solid loses energy- exothermicDisorder to order = lose energy
16 The sign of the enthalpy reactions For an endothermic reaction, heat energy is _____________.When the Hreactants is subtracted from the ________Hproduct, a ________ value for ΔHrxn is obtained.Enthalpy changes for endothermic reactions are always_______________.absorbedlargerpositivepositive
17 Notice the phase change Provide the enthalpy change reaction for cold pack with NH4NO3NH4NO3(s)NH4+ (aq)+NO3- (aq)ΔH= 27 kJNotice the phase change(s) (aq) + (aq)Solid to liquid gains energy- endothermicOrder to disorder gains energy
18 Endothermic Exothermic Exothermic Endothermic Exothermic Identify the reaction as endothermic or exothermic-PAY ATTENTION TO PHASE CHANGESC2H5OH (l) C2H5OH(g)NH3(g) NH3(l)Br2(l) Br2(s)NaCl (s) NaCl (l)C5H12 (g) + 8O2 (g) 5CO2 (g) + 6H2O(l)EndothermicExothermicExothermicEndothermicExothermic
21 The Flask and everything around the flask. Solution + surroundings 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 solutionThe Flask and everything around the flask.Solution + surroundings
23 Thermochemical equations Are balanced chemical equations that include physical states of all reactants and products AND the energy change ∆H.NH4NO3(s)NH4+ (aq)+NO3- (aq)ΔH= 27 kJ
24 Types of enthalpy ∆H(comb) ∆H(vap) ∆H(fus) Change in heat with combustionChange in heat with vaporizationChange in heat with fusion
25 Thermochemical equations for changes in state Consider:H2O(l) H2O(g)ΔH(vap)= 40.7 kJWhat is happening?Its vaporizing.What ∆H would you use? Would it be + or -?Positive- endothermic
26 Thermochemical equations for changes in state Consider:H2O(s) H2O(l)ΔH(fus)= 6.01 kJWhat is happening?Its melting.What ∆H would you use? Would it be + or -?Positive- endothermic
27 Pay attention to the signs ∆Hvap = -∆Hcond∆Hfus = -∆HsolidSo -∆Hcond for water isH2O(g) H2O(l)ΔH(cond)= kJSo -∆Hsolid for water isH2O(l) H2O(s)ΔH(fus)= kJMakes sense- both are exothermic -∆H
28 Calculating energy released in a reaction How much heat is released when 54.0 g of glucose (C6H12O6) is burned?C6H12O6 (s) + 6O2(g) 6CO2(g) + 6H2O(l) ∆H comb= kJ∆H comb= kJ is per mole of glucoseConvert gram to mole54.0g glucose1 mole glucose= 0.3 mol180 g glucose= 0.3 mol X ∆H comb =842 kJ
29 You Try!!1. Calculate the heat required to melt 25.7 g of solid methanol at its melting point.Which ∆H would you use?∆H (fus) because its melting. So 3.22 its is.∆H(fus) be positive or negative?∆H (fus) be positive. ∆H (fus)= 3.22 per mole.
30 You Try!!1. Calculate the heat required to melt 25.7 g of solid methanol at its melting point.∆Hfus= 3.22 kJ is per mole of methanolConvert gram to mole25.7g methanol1 mole methanol= mol32 g methanol= mol X ∆H fus =2.58 kJ
31 You Try!! Which ∆H would you use? ∆H(vap) be positive or negative? 2. How much heat is evolved when 275g of ammonia gas condenses to a liquid at its boiling point?Which ∆H would you use?∆H (vap) because its condensing. So 23.3 its is.∆H(vap) be positive or negative?∆H (vap) be negative. ∆H (vap)= per mole.
32 You Try!!2. How much heat is evolved when 275g of ammonia gas condenses to a liquid at its boiling point?∆Hvap= kJ is per mole of ammoniaConvert gram to mole275g ammonia1 mole ammonia= 16.2 mol17 g ammonia= 16.2 mol X ∆H vap=377 kJ
33 You Try!! 12880 ÷ -891 =14.5 moles of methane 14.5mol methane 3. What mass of methane must be burned in order to liberate 12880kJ of heat? Methane (CH4) ∆Hcomb= kJ/mol÷ =14.5 moles of methane14.5mol methane16 g methane= 232 g1 mole methane
34 You Try!!2. How much heat is evolved when 275g of ammonia gas condenses to a liquid at its boiling point?∆Hvap= kJ is per mole of ammoniaConvert gram to mole275g ammonia1 mole ammonia= 16.2 mol17 g ammonia= 16.2 mol X ∆H vap=377 kJ
35 Tonight Finish backside w.s AND Pre-lab Questions
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