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IB1 Chemistry Energetics 1 Enthalpy changes

IB1 Chemistry Energetics 1 Enthalpy changes. Why do chemical reactions get hot (or cold)?. What is the difference between energy and enthalpy? What is the difference between temperature and heat? How much heat does it take to increase the temperature of a substance?

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IB1 Chemistry Energetics 1 Enthalpy changes

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  1. IB1 ChemistryEnergetics 1Enthalpy changes

  2. Why do chemical reactions get hot (or cold)? • What is the difference between energy and enthalpy? • What is the difference between temperature and heat? • How much heat does it take to increase the temperature of a substance? • What is the difference between enthalpy change and standard enthalpy change? • How is calorimetry used to measure enthalpy changes? • How is standard enthalpy change calculated from a temperature change?

  3. Exothermic and endothermic reactions Ammonium nitrate and water Iron and oxygen

  4. Temperature- average KE per particle higher speed  higher temperature more particles at same speed  same temperature

  5. Enthalpy, H • Energy stored in reactants (in Joules) • PE and KE of particles + energy to make space for substance Image: https://en.wikipedia.org/wiki/File:Ammonium_Nitrate.jpg

  6. Cold pack • The temperature of the cold pack decreases during the reaction • The temperature of the cold pack increases during the reaction • The cold pack transfers cold to the person touching it • Heat is taken in from the person to the cold pack • The cold pack has less energy and lower enthalpy after it is used

  7. Exothermic reactions Enthalpy, J reactants ∆H products reaction coordinate

  8. Endothermic reactions Enthalpy, J products ∆H reactants reaction coordinate

  9. Standard enthalpy change of a reaction ∆H° to compare reactions in kJ/mol measured at 298K and 1atm

  10. Using temperature to calculate ∆H° Heat energy = mass x specific heat capacity x temperature change Q = mc∆T

  11. Calculating standard enthalpy change What is the enthalpy change in kJ per mole if 45kJ are given out when 0.8g of methane are burned? What is the enthalpy change in kJ per mole if 1.6g of methanol are used to heat 200mL water from 20C to 38C?

  12. Links • Ionic bonding http://www.teachersdomain.org/asset/lsps07_int_ionicbonding/ • Covalent bonding http://www.teachersdomain.org/asset/lsps07_int_covalentbond/

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