2.  Chemical rxns involve changes in energy – Breaking bonds requires energy – Forming bonds releases energy  These energy changes can be in the form of heat – Heat is the flow of chemical energy  The study of the changes in energy in chem rxns is called thermochemistry.  The energy involved in chemistry is real and generally a measurable value  Chemical rxns involve changes in energy – Breaking bonds requires energy – Forming bonds releases energy  These energy changes can be in the form of heat – Heat is the flow of chemical energy  The study of the changes in energy in chem rxns is called thermochemistry.  The energy involved in chemistry is real and generally a measurable value INTRO TO THERMOCHEMISTRY

3. WHAT IS HEAT?  Hot & cold, are automatically associated with the words heat and temperature –Heat & temp are NOT synonyms –The temperature of a substance is directly related to the energy of its particles, specifically its:  Hot & cold, are automatically associated with the words heat and temperature –Heat & temp are NOT synonyms –The temperature of a substance is directly related to the energy of its particles, specifically its:  The Kinetic Energy defines the temperature –Particles vibrating fast = hot –Particles vibrating slow = cold  The Kinetic Energy defines the temperature –Particles vibrating fast = hot –Particles vibrating slow = cold

4.  Vibrational energy is transferred from one particle to the next – One particle collides with the next particle and so on; and so on – down the line  Vibrational energy is transferred from one particle to the next – One particle collides with the next particle and so on; and so on – down the line An Ice Cold Spoon A Hot Spoon

5. 2 Hot Spoons  Thermal energy is the total energy of all the particles that make up a substance – Kinetic energy from vibration of particles – Potential energy from molecular attraction (within or between the particles)  Thermal energy is dependent upon the amount or mass of material present (KE =½mv 2 )  Thermal energy is the total energy of all the particles that make up a substance – Kinetic energy from vibration of particles – Potential energy from molecular attraction (within or between the particles)  Thermal energy is dependent upon the amount or mass of material present (KE =½mv 2 )  Thermal energy is also related to the type of material

6.  Thermal energy can be transferred from object to object through direct contact – Molecules collide, transferring energy from molecule to molecule – http://www.hk-phy.org/contextual/heat/hea/condu/conduction_e.html http://www.hk-phy.org/contextual/heat/hea/condu/conduction_e.html  Thermal energy can be transferred from object to object through direct contact – Molecules collide, transferring energy from molecule to molecule – http://www.hk-phy.org/contextual/heat/hea/condu/conduction_e.html http://www.hk-phy.org/contextual/heat/hea/condu/conduction_e.html

7.  Thermal energy can be transferred from object to object through direct contact – Molecules collide, transferring energy from molecule to molecule  Thermal energy can be transferred from object to object through direct contact – Molecules collide, transferring energy from molecule to molecule

8. DEFINITION THE FLOW OF THERMAL ENERGY FROM SOMETHING WITH A HIGHER TEMP TO SOMETHING WITH A LOWER TEMP UNITS MEASURED IN JOULES OR CALORIES TYPES THROUGH WATER OR AIR = CONVECTION THROUGH SOLIDS = CONDUCTION TRANSFERRED ENERGY BY COLLISION WITH PHOTON = RADIANT ENERGY

9. HEAT CAPACITY  The measure of how well a material absorbs or releases heat energy is its heat capacity – It can be thought of as a reservoir to hold heat, how much it holds before it overflows is its capacity  Heat capacity is a physical property unique to a particular material – Water takes 1 calorie of energy to raise temp 1 °C  The measure of how well a material absorbs or releases heat energy is its heat capacity – It can be thought of as a reservoir to hold heat, how much it holds before it overflows is its capacity  Heat capacity is a physical property unique to a particular material – Water takes 1 calorie of energy to raise temp 1 °C

10. SPECIFIC HEAT CAPACITY  The amount of energy it takes to raise the temp of a standard amount of an object 1°C is that object’s specific heat capacity (C p ) – The standard amount =1 gram  Specific heats can be listed on data tables – Smaller the specific heat  the less energy it takes the substance to feel hot – Larger the specific heat  the more energy it takes to heat a substance up (bigger the heat reservoir)  The amount of energy it takes to raise the temp of a standard amount of an object 1°C is that object’s specific heat capacity (C p ) – The standard amount =1 gram  Specific heats can be listed on data tables – Smaller the specific heat  the less energy it takes the substance to feel hot – Larger the specific heat  the more energy it takes to heat a substance up (bigger the heat reservoir)

11. CHEMICAL RXNS  There are 2 types of chemical rxns – Exothermic rxns  rxns in which heat energy is a product – Endothermic rxns  rxns in which heat energy is a reactant  Exothermic rxns typically feel warm as the rxn proceeds – Gives off heat energy, sometimes quite alot  Endothermic rxns typically feel cooler the longer the rxn proceeds – Absorbs heat energy, sometimes enough to get very cold  There are 2 types of chemical rxns – Exothermic rxns  rxns in which heat energy is a product – Endothermic rxns  rxns in which heat energy is a reactant  Exothermic rxns typically feel warm as the rxn proceeds – Gives off heat energy, sometimes quite alot  Endothermic rxns typically feel cooler the longer the rxn proceeds – Absorbs heat energy, sometimes enough to get very cold

13. NH 4 NO 3 +H 2 O+ 752kJ  NH 4 OH+HNO 3  Endothermic rxn –Similar system as what is found in cold packs

14. C3H8C3H8 C3H8C3H8 + + 5O 2 2043kJ   3CO 2 4H 2 O + + + +  Exothermic rxn –To a cold camper, the important product here is the heat energy

15. HEATHEATHEATHEATHEATHEATHEATHEAT

16. Enthalpy  Defined as the heat of a reaction (H)  Δ H – Change in enthalpy is equal to the energy flow as heat of a chemical reaction  Is a state function it is independent of the pathway  Defined as the heat of a reaction (H)  Δ H – Change in enthalpy is equal to the energy flow as heat of a chemical reaction  Is a state function it is independent of the pathway

17.  Most common version of enthalpy is when we have a change in enthalpy (  H)  The enthalpy absorbed or gained (changed) in a rxn is dependent on the amount of material reacting – Amount is usually in the form of moles – We can use the coefficient ratios to energy ratios to calculate how much energy a reaction used or produced  Most common version of enthalpy is when we have a change in enthalpy (  H)  The enthalpy absorbed or gained (changed) in a rxn is dependent on the amount of material reacting – Amount is usually in the form of moles – We can use the coefficient ratios to energy ratios to calculate how much energy a reaction used or produced CHANGE IN ENTHALPY

18. (For Example) How much heat will be released if 1.0g of (H 2 O 2 ) decomposes in a bombardier beetle to produce a defensive spray of steam (For Example) How much heat will be released if 1.0g of (H 2 O 2 ) decomposes in a bombardier beetle to produce a defensive spray of steam 2H 2 O 2  2H 2 O + O 2  Hº =+190kJ USING  H IN CALCULATIONS  Chemical reaction equations are very powerful tools. – Given a rxn equation with an energy value, We can calculate the amount of energy produced or used for any given amount of reactants.  Chemical reaction equations are very powerful tools. – Given a rxn equation with an energy value, We can calculate the amount of energy produced or used for any given amount of reactants.

19.  H = FINAL TEMP – INITIAL TEMP FINAL TEMP – INITIAL TEMP SPECIFIC HEAT SPECIFIC HEAT MASS  We can also track energy changes due to temp changes, using  H=mC p  T:  If the temp difference is positive – The rxn is exothermic because the final temp is greater than the initial temp – So the enthalpy is positive  If the temp difference is positive – The rxn is exothermic because the final temp is greater than the initial temp – So the enthalpy is positive  if the temp change is negative – makes the enthalpy negative – the rxn absorbed heat into the system, so it’s endothermic  if the temp change is negative – makes the enthalpy negative – the rxn absorbed heat into the system, so it’s endothermic

20. CALORIMETRY  Calorimetry is the process of measuring heat energy – Measured using a device called a calorimeter – Uses the heat absorbed by H 2 O to measure the heat given off by a rxn or an object  The amount of heat soaked up by the water is equal to the amount of heat released by the rxn  Calorimetry is the process of measuring heat energy – Measured using a device called a calorimeter – Uses the heat absorbed by H 2 O to measure the heat given off by a rxn or an object  The amount of heat soaked up by the water is equal to the amount of heat released by the rxn  H SYS =-  H SUR  H sys is the system or what is taking place in the main chamber (rxn etc.) And  H sur is the surroundings which is generally water.

21. A COFFEE CUP CALORIMETER A COFFEE CUP CALORIMETER A BOMB CALORIMETER A BOMB CALORIMETER USED WHEN TRYING TO FIND THE AMOUNT OF HEAT PRODUCED BY BURNING SOMETHING. USED WHEN TRYING TO FIND THE AMOUNT OF HEAT PRODUCED BY BURNING SOMETHING. USED FOR A REACTION IN WATER, OR JUST A TRANSFER OF HEAT. USED FOR A REACTION IN WATER, OR JUST A TRANSFER OF HEAT.

22.  H SYS = = -  H SUR + SIGN MEANS HEAT WAS ABSORBED BY THE RXN + SIGN MEANS HEAT WAS ABSORBED BY THE RXN - SIGN MEANS HEAT WAS RELEASED BY WATER - SIGN MEANS HEAT WAS RELEASED BY WATER  With calorimetry we use the sign of what happens to the water – When the water loses heat into the system it obtains a (-) sign  With calorimetry we use the sign of what happens to the water – When the water loses heat into the system it obtains a (-) sign CALORIMETRY

23. HEATHEATHEATHEAT

24.  With calorimetry we use the sign of what happens to the water – When the water gains heat from the system it obtains a (+) sign  With calorimetry we use the sign of what happens to the water – When the water gains heat from the system it obtains a (+) sign -  H SYS = =  H SUR - SIGN MEANS HEAT WAS RELEASED BY THE RXN - SIGN MEANS HEAT WAS RELEASED BY THE RXN + SIGN MEANS HEAT WAS ABSORBED BY WATER + SIGN MEANS HEAT WAS ABSORBED BY WATER CALORIMETRY

25. HEATHEATHEATHEAT

26.  You calculate the amount of heat absorbed by the water (using  H= mC  T)  Which leads to the amount of heat given off by the rxn – you know the mass of the water (by weighing it) – you know the specific heat for water (found on a table) – and you can measure the change in the temp of water (using a thermometer)  You calculate the amount of heat absorbed by the water (using  H= mC  T)  Which leads to the amount of heat given off by the rxn – you know the mass of the water (by weighing it) – you know the specific heat for water (found on a table) – and you can measure the change in the temp of water (using a thermometer) CALORIMETRY