Beaker with hot water

1. Beaker with hot water • Exothermic • “exiting heat” exiting from ______ the water/beaker warm If you were the hand, you sense______ If you were the beaker, you sense_________ cool

2. Beaker with cold water • Endothermic “entering heat” • entering from _ the hand If you were the hand you sense _______ cool If you were the beaker, you sense______ _warm_____

3. What changes happen using this size beaker?

4. Primary Factors • Mass • Temperature

5. NOTICE Heat that flows includes temperature, but is not the same as temperature.

6. Symbols • m = mass • T = temperature • q = heat flow (- = out, + = in) • c = specific heat(ability of pure • substance to retain heat) • C = heat capacity(ability of • object to retain heat)

7. Mathematical Relationships • q = m x c x ΔΤ • q = C x ΔΤ

9. Hot metal warms the water Metal transfers heat to water Water gains heat from metal Metal heat loss equals water heat gain Symbolic Expression -q(metal) = q (water) -(mxcxΔΤ (metal))=(mxcxΔΤ (water))

10. BEYOND CALORIMETRY ENERGY CHANGES IN REACTIONS ENTHALPY SYMBOL H ENTHALPY CHANGE Δ H

11. Remember??? • Exothermic- ΔH

12. Remember?? • Endothermic ΔH

13. Thermochemical Equations H2(g) + Cl2(g) →2 HCl(g)ΔH = - 185 kJ NOTICE: phases must be included coefficients represents moles sign of ΔH indicates direction of heat flow products, reactants assumed to be 25 oC

14. Thermochemical Rules size of ΔH directly proportional to moles ΔH for reverse reaction - opposite sign ΔH same regardless of number of steps

15. Standard Enthalpy of Formation Can predict heat flow for ANY equation Symbol - ΔHo 1 atm, 1 M and 25 oC f

16. Calculating Standard Enthalpies ΔHo = ∑ΔHo products - ∑ΔHo reactants f f Elements in standard state - omitted Must take coefficients into account Practice #24 page 221

17. First Law of Thermodynamics- “total energy of a system is the sum of all energy and work going into and out of that system”. heat work ΔE(system) = -ΔE(surroundings)ΔE = q + w w q -w -q system