* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Thermochemistry
Survey
Document related concepts
Dynamic insulation wikipedia , lookup
Building insulation materials wikipedia , lookup
Solar water heating wikipedia , lookup
Thermoregulation wikipedia , lookup
Solar air conditioning wikipedia , lookup
Intercooler wikipedia , lookup
Heat exchanger wikipedia , lookup
R-value (insulation) wikipedia , lookup
Copper in heat exchangers wikipedia , lookup
Heat equation wikipedia , lookup
Cogeneration wikipedia , lookup
Transcript
Energy change that occurs during a chemical reaction and/or changes in state A form of energy Flows from warmer objects to cooler objects Represented by the variable “q” Measured by units: calorie or joule 1 J = 0.2390 cal 4.184 J = 1 cal 1000 cal = 1 kilocalorie = 1 Cal Exothermic Process ◦ Energy flows from the system into the surroundings Endothermic Process ◦ Energy flows from the surroundings into the system Conservation of Energy ◦ Energy is not created or destroyed in a physical or chemical process ◦ If energy in a system decreases, then the energy of the surroundings increases by the same amount Amount of heat needed to increase the temperature of an object exactly 1 ˚C ◦ Depends on mass and chemical composition ◦ Greater mass = greater heat capacity Specific Heat Capacity, Cp (Specific Heat) ◦ Amount of heat needed to raise 1 g of a substance by 1 ˚C ◦ Metals have low specific heats ◦ Water has a relatively high specific heat q= m x Cp x ΔT Cp is the variable for specific heat ◦ Could be in units of J/(g•˚C) or cal/(g•˚C) q is the variable for heat (joules or calories) M is the variable for mass (grams) ΔT (Tf – Ti) is the variable for change in temperature (˚C) Enthalpy (H) is the heat content of a system at constant pressure ◦ Heat absorbed or released by a system (constant pressure) is the change in enthalpy, ΔH ◦ We will only work with a constant pressure scenario…therefore, q = ΔH Calorimetry ◦ Measurement of heat flow into/out of a system ◦ Calorimeter is the device used to measure heat flow If a system gains heat, that amount of heat was lost by the surroundings… qsys = - qsurr (the negative sign represents loss) ΔH = qsys = - qsurr = m x Cp x ΔT Exothermic reactions have a negative value for ΔH Endothermic reactions have a positive value for ΔH A chemical equation that includes enthalpy change Can be either a “reactant” ◦ Endothermic 2NaHCO3 + 129 kJ Na2CO3 + H2O + CO2 or 2NaHCO3 Na2CO3 + H2O + CO2 ΔH = 129 kJ Or a “product” ◦ Exothermic CaO + H2O Ca(OH)2 + 65.2 kJ or CaO + H2O Ca(OH)2 ΔH = -65.2 kJ How much heat in joules is required to raise 1000g of water from 20 °C to 55 °C ? When 435 J of heat is added to 3.4 g of olive oil at 21 °C, the temperature increases to 85 °C. What is the specific heat of olive oil? How much heat in kilojoules is required to raise the temperature of 250.0 g of mercury 52 °C? (Cp of Hg = 0.14 J/g* °C)