Catalyst.

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Presentation transcript:

Catalyst

Calorimetry Hook

Today’s Learning Target LT. 5.10 – Using a heating curve and calorimetry, I can hypothesize and calculate the energy required to heat and/or cool a system and the amount of heat that is produced from this process.

Pre – Lab Lecture Please read the lab introduction and procedures

Lab Worktime

Lecture 5.4 – Calorimetry

Measuring Heat Flow Into/Out of a System Up to this point we have talked about ΔH and q in theoretical terms. How do we go into the lab and measure these quantities? The measurement of heat flow is the science of calorimetry. Heat flow is measured with a calorimeter.

Specific Heat The amount of of heat it takes to change the temperature is dependent on the substance being studied The heat capacity is the amount of energy required to raise a substances temperature 1 oC The molar heat capacity (Cm) is the amount of energy to raise one mole of substance, one degree C. The specific heat (Cs) describes the amount of energy that is required to change one gram of a substance, one degree C. Give the example of a piece of metal and a sample of water. Which heats up faster? Why?

Calculating Heat Therefore, if specific heat is known (it is a constant), then heat can be calculated: For a phase change, heat can be calculated by: Depends on units of ΔH

Class Example How much heat is needed to warm 250 g of water from 22 oC to 98 oC? Note, the specific heat of water is 4.18 J/(g x oC)?

Table Talk Large beds of rocks are used in some solar – heated homes to store heat. Assume to specific heat of the rocks is 0.82 J/(g x oC). Calculate the amount of heat absorbed by 50.0 kg of rocks when they are heated from 20.0 oC to 32.0 oC.

Multiple Step Calorimetry Problems When doing multiple steps for a single heating, think of the heating curve. Each portion of the line represents a different q term Can solve for qtotal by adding up q terms for a problem e d Heat Added (J) c b qtotal = qa + qb + qc + qd + qe a Time (s)

Class Example How much energy is needed to change 150 g of solid ice from 0 oC to 50 oC? The specific heat of liquid water is 4.184 J/(g x oC) and the ΔHfusion = 6.0 kJ/mol

Table Talk ΔHcondensation = -40.7 kJ/mol Cs, liquid = 4.184 J/(g x oC) How much heat is required to convert a 120 g snowman from – 10.0 C to 108 C? Note the following terms: ΔHfusion = 6.0 kJ/mol Cs, solid = 2.1 J/(g x oC) ΔHcondensation = -40.7 kJ/mol Cs, liquid = 4.184 J/(g x oC) Cs, gas = 1.7 J/(g x oC)

Constant Pressure Calorimetry When these measurements are done in a typical room, pressure is constant, so the data can be used to calculate ΔH. When you are running these reactions in a solution, you are measuring the qsoln, but we want to measure qrxn. Therefore, if a solution gains heat it must have been lost by the reaction (and vice versa):

Table Talk Using the data from the lab, calculate the qrxn. Note – You need to add qcal and qsolution to obtain qrxn

Calculating ΔHrxn from qrxn As previously mentioned, if qrxn is known, then ΔHrxn can be calculated

Table Talk Using the data from the lab, calculate ΔHrxn

Bomb (Constant Volume) Calorimetry Oftentimes, we need to run a reaction under constant volume conditions, rather than constant pressure conditions. Often used with combustion reactions We then calculate qrxn by the equation: The heat transferred corresponds to the ΔE

Class Example The combustion of methylhydrazine, a liquid in rocket fuel, produces N2, CO2, and H2O: 2 CH6N2 + 5 O2  2 N2 + 2 CO2 + 6 H2O When 4.00 g of methylhydrazine is combusted in a bomb calorimeter the temperature of the calorimeter increases from 25.00 oC to 39.50 oC. IN a separate experiment the hear capacity of the calorimetor is measured to be 7.794 kJ/oC. Calculate the heat of reaction for the combustion of 1 mole of CH6N2

Table Talk A 0.5865 g of lactic acid (HC2H5O3) is burned in a calorimeter whose heat capacity is 4.812 kJ/oC. The temperature increases from 23.10 oC to 24.95 oC. Calculate the heat of combustion of lactic acid per 1 mole.

Problem Set Work Time This problem set will be due Thursday/Friday Please use the remaining time to collaborate with one another on how to complete these problems

Closing Time Read 5.5 Problem Set 5.4 Post Lab questions for Lab 11 due Thursday/Friday