Thermochemistry

ThermochemistryChemistryMs. PielaThermochemistry Heat transfers in chemical reactionsEnergyDefinition: The capacity to do work or supply heatBasic Types: Mechanical, Electrical, Potential, Kinetic

Chemical Potential EnergyEnergy that is stored within chemical bondsDetermined by the arrangement and bonding of atomsExamples: Gasoline, Food, etc

Exothermic & EndothermicExothermic processes (exits)Heat flows out of a system

SystemSurroundingsExothermic and EndothermicSystem loses heat (negative sign)Examples: Explosions!, Sun, Fire

Exothermic and EndothermicEndothermic processes (enter)Heat is absorbed from surroundingsSystemSurroundingsExothermic and endothermicSystem gains heat (positive sign), Heat change is > 0Examples: Boiling water, ice melting

Heat Energy transfers due to temperature differences between objectsFlows from hot to cold until temperature equilibrium is reached

Law of Conservation of Energy Energy cannot be created or destroyed, only transferredCan be transformedExample:Units of HeatCalorie (cal) the amount of heat needed to raise 1 gram of water 1 CHeat calorie is not to be confused with dietary calories1 dietary Calorie = 1 kcal = 1000 calJoule (J) metric unit of heat and energy

1 cal = 4.184 JConversion Factor! Woo! Conversion PracticeIt takes 50.2 J to raise the temperature of a 100.0 g piece of glass. How many calories is this?Conversation PracticeA small chocolate bar has about 210,000 calories. How many Joules is this?Specific Heat The amount of heat required to raise 1 gram of a substance 1 CHeat capacity is the amount of heat required to raise a substance 1 C

VS.Specific Heat Equationq = heat (J or cal)m = mass (g)C = specific heatT = Change in Temp. (C) q = mCT

Specific Heat Application: Land vs. WaterSpecific heat plays a role in buffering climatesSpecific heat of land = 0.8 J/g CSpecific heat of water = 4.184 J/g CHow does this help buffer climates?Water heats up slower and cools down slowly, releasing heat gradually

Table of Specific Heat CapacitiesOn the notes, youll see a table of specific heat capacities for common metals.Well be using these throughout all the problems in this section, so keep it handy!Specific Heat Example 1A 1.55 g piece of stainless steel absorbs 141 J of heat when its temperature increases by 178 C. What is the specific heat of stainless steel?.511 J/g CSpecific Heat Example 2How much heat is required to raise the temperature of 250.0 g of mercury from 52 C to 60 C?280 JSpecific Heat Example 3If the initial temperature of a 10.0 g substance is 20.0 C and 100.0 J of heat are absorbed, what is the final temperature? The specific heat of the substance is 1.15 J/g C.28.7 C