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What is the difference between heat and temperature? HEAT is energy that transfers from one object/substance to another TEMPERATURE is a measure of the.

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Presentation on theme: "What is the difference between heat and temperature? HEAT is energy that transfers from one object/substance to another TEMPERATURE is a measure of the."— Presentation transcript:

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2 What is the difference between heat and temperature? HEAT is energy that transfers from one object/substance to another TEMPERATURE is a measure of the amount of energy an object/substance has

3 A. Energy Transformations Energy that is stored in the chemical bonds of a substance is called CHEMICAL POTENTIAL ENERGY Heat ALWAYS flows from hot to cold

4 B. Endothermic and Exothermic Processes System=the reaction Surroundings=everything around the reaction Surroundings Law of Conservation of Energy- energy can be neither created nor destroyed System

5 B. Endothermic and Exothermic Processes Endothermic Process- heat is absorbed from the surroundings Endo = Into Endothermic processes are represented by a positive q HEAT

6 B. Endothermic and Exothermic Processes Exothermic process- heat is released into the surroundings Exo = Exit Exothermic processes are represented by a negative q HEAT

7 C. Measuring Heat Flow Two Common Units Joule calorie 1J = cal J = 1 cal 1Calorie = 1 kilocal = 1000 cal

8 D. Heat Capacity and Specific Heat Heat Capacity depends on: The mass of the object The chemical composition of the object the amount of heat needed to increase the temperature of an object by 1 o C Specific heat capacity- amount of heat needed to raise the temperature of 1g by 1 o C

9 D. Heat Capacity and Specific Heat C = q / (m X ΔT) C =Specific Heat q = heat (joules or calories) m = mass (grams) ΔT = change in temperature The change in temperature can be measure in Kelvin or degrees Celsius

10 The temperature of a 95.4g piece of copper increases from 25.0 o C to 48.0 o C when it absorbs 849 J of heat. What is the specific heat of copper? Known: m= 95.4g q=849 J ΔT= =23.0 o C Work: C= 849J/ (95.4g)(23.0 o C)= J/(g· o C)

11 E. Calorimetry Measures the heat flow into or out of a system Heat released by the system is equal to heat absorbed by the surroundings ENTHALPY: (H) the heat constant of a system at constant pressure

12 E. Calorimetry The terms heat and enthalpy change are interchangeable q = ΔH q sys = ΔH = -m x C x ΔT Negative enthalpy = exothermic Positive enthalpy = endothermic

13 When 25.0mL of water containing HCl at 25.0 o C is added to 25.0mL of water containing NaOH at 25.0 o C in a calorimeter a rxn occurs. Calculate the enthalpy change (in kJ) during the rxn if the highest temperature observed was 32.0 o C. Assume all densities =1g/mL KNOWN: C water =4.18J/g o C V=25.0mL+25.0mL ΔT=7 o C Density= 1g/mL ΔH = ?

14 m= (50mL) x (1.00g/mL) = 50g ΔT= T F – T i = 32.0 – 25.0 =7.0 ΔH= -mCΔT= -(50.0g)(4.18J/g o C)(7.0 o C) ΔH= J = -1500J = -1.5kJ

15 F. Thermochemical Equations In a thermochemical equation, the enthalpy of change for the reaction can be written as either a reactant or a product Endothermic (positive ΔH) 2NaHCO kJ Na 2 CO 3 + H 2 O + CO 2 Exothermic (negative ΔH) CaO + H 2 O Ca(OH) kJ

16 G. Heat of Combustion The heat of reaction for the complete burning of one mole of a substance Written the same was as change in enthalpy

17 Write the thermochemical equation for the oxidation of Iron (III) if its ΔH= kJ Fe(s) + O 2 (g) Fe 2 O 3 (s) How much heat is evolved when 10.00g of Iron is reacted with excess oxygen? g Fe 55.85g Fe 1 mol = mol Fe mol Fe 4 mol Fe 1652 kJ =73.97 kJ of heat


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