Presentation on theme: "Unit 5 ENERGY 5.4 What are endothermic and exothermic reactions?"— Presentation transcript:
1 Unit 5 ENERGY 5.4 What are endothermic and exothermic reactions? April 1, 2011AIM: How do we identify a substance to be exothermic or endothermic?q = mcΔT1. What much heat is released when 10 g of water are cooled from 20˚C to 10˚C?2. What much heat is absorbed when 10 g of water are heated from 10˚C to 20˚C?3. What is the difference between these two problems above?DO NOW:q=(10g)(4.18J/g•oC)(-10oC) = -418Jq=(10g)(4.18J/g• oC)(10oC) = 418JOne has negative heat and the other has positive heat
2 Heat of fusion and Heat of vaporization REVIEWHeat of fusion and Heat of vaporizationExplain the following in a coherent, well-written paragraph1. Explain why we use the q=Hf and q=Hv2. How we decide whether to use constant for the heat of fusion OR the heat of vaporization3. Explain why we can’t use Table B for any other substance besides water.4. Explain why temperature does not change during a phase change but heat is required for the phase change.
3 ENDOTHERMIC melting: vaporization: sublimation: take in energy (heat)heat is absorbedheat is a positive numberENDOTHERMIC REACTIONSAMPLE IS HEATEDmelting:vaporization:sublimation:solid liquid (ice cream melting)liquid gas (boiling water)solid gas
4 EXOTHERMIC freezing: liquid solid (making ice cubes) v condensation: release energy (heat)heat exitsheat is a negative numberEXOTHERMIC REACTIONSAMPLE IS COOLEDfreezing:liquid solid (making ice cubes) vcondensation:gas liquid (rain)gas soliddeposition:
5 Let’s try someq = mcΔT1. What is the total number of joules of heat energy are absorbed when 100g of water are heated from 20˚C to 30˚C?1. asking me to find out HOW MANY J q2. pick out important information100g of waterhow much stuff mtemperature change ΔT30oC to 20oCSpecific heat of water c4.18 J/g • oC