07-02-journal-flvs-chemistry-module-7-guided-notes-all-filled-out
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07 02 journal - FLVS chemistry module 7 guided notes allfilled outChemistry (Boca Raton Community High School (FL))Scan to open on StudocuStudocu is not sponsored or endorsed by any college or university07 02 journal - FLVS chemistry module 7 guided notes allfilled outChemistry (Boca Raton Community High School (FL))Scan to open on StudocuStudocu is not sponsored or endorsed by any college or universityDownloaded by Ronin Steven (roninsteven9@gmail.com)lOMoARcPSD|46891182
Chemistry Journal 7.2Enthalpy ValuesDriving Questions: How do scientists calculate enthalpy for physical and chemical changes, andhow does that help distinguish between endothermic and exothermic changes?Key Ideas andTermsNotesFQ: How is specific heat capacity related to temperature?What is specific heat capacity?Different types of matter require different amounts of energy to change in temperature. This physical property of matter is known as specific heat capacity-the quantity of heat required to raise the temperature of one gram of a substance by one degree CelsiusWhy is specific heat capacity an intensive property?It is an intensive property because the amount of the substance does not change its specific heat capacityHow does a changein mass affect how much thermal energy is needed to change the temperature of a substance?However, a difference in mass does impact how much thermal energy must be absorbed before a change in temperature occurs. For instance, when the same amount of heat is applied, an ocean will take a lot longer to change temperature than a small lake.Video: Specific Heat CapacityWhat units of measurement are used to measure specific heat capacity?Specific heat capacity is defined as the amount of heat required to raise the temperature of one gram of a particular substance by one degree Celsius. It is measured in joules per gram degrees Celsius. It can also be measured in joules per gram Kelvin. Specific heat capacity has various applications. It is used in thermodynamics in materials testing, and can also be used forensically to identify elements and compounds.What is the formula for specific heat C = q/m x ∆T(Means specific heat, or C, equals heat generated by the temperature Downloaded by Ronin Steven (roninsteven9@gmail.com)lOMoARcPSD|46891182
capacity?change, or Q, divided by the mass of substance times the change in temperature.)Does low specific heat equal lower melting point? Explain why or why not.It's a common misconception that low specific heat equals a lowermelting point, and vice versa. It isn't true. There are metals like copperand iron that have a low specific heat, but they have high melting points.This is why iron and copper skillets are used for cooking—they heat onthe stove without melting onto it. You can melt ice and evaporate water ina metal pot, but there is no change of state to the pot itself.FQ: How are energy transfers calculated using a temperature change?How do chemists calculate energy transfers in an unknown sample?The energy transfer of an unknown sample can be calculated using the specific heat capacity of the sample, the temperature change observed during the reaction, and the mass of the sample. Below, is how enthalpy relates to specific heat capacity and how to calculate it.Video: Calculating EnthalpyWhat is the equation to calculate enthalpy?q = m x C x ∆TShow how to use the enthalpyequation from the video example. For example, how much heat energy is required to raise the temperature of 500 grams of lead from 20 degrees Celsius to 45 degrees Celsius?Downloaded by Ronin Steven (roninsteven9@gmail.com)lOMoARcPSD|46891182
Describe each variable of the enthalpy equation. Putting the values into the formula, q, or heat energy, equals the mass of substance, times the specific heat capacity of substance, times the change intemperature, degrees Celsius to find your answer.q: the heat gained (positive) or lost (negative) by the system, in joulesm: the mass of the sample, in gramsc: the specific heat capacity of the sample, in joules per gram per degree Celsius Jg °C△T: the change in temperature, in degrees CelsiusHow is change of temperature determined for the enthalpy equation?When using the specific heat capacity equation to calculate enthalpy, the change in temperature (△T) can be determined by subtracting the initial temperature of a substance from the final temperature.A flask containing 855 grams of water was heated over a Bunsen burner. If the temperature of the water was raised from 21.0 to 85.0 degrees Celsius, how much heat (in joules) did the water absorb? Describe the steps.The specific heat capacity of liquid water is 4.184 J/g ⁰C.What we know:m = 855 gc = 4.184 Jg °CΔT = 85.0 °C − 21.0 °C = 64.0 °CWhat we need:Enthalpy (q)q = m × c × △Tq = 855g× 4.184 J /g °C× 64.0°Cq = 228,948.48 JThe water absorbed 229,000 joules, or 229 kilojoules, of energy.Use the common specific heat capacities table to help you solve the practice problems below. Be sure to include a copy of the table to your chemistry journal.Downloaded by Ronin Steven (roninsteven9@gmail.com)lOMoARcPSD|46891182
A frying pan with 5grams of vegetable oil is heated on a stove top. If the temperature of the oil increases from 25.0 °C to 95.0 °C, how much energy does the oil absorb?q = m × c × △Tq = 5 g × 2.00 Jg °C × (95.0 °C − 25.0 °C)q = 700 JThe oil absorbs 700 joulesof energy.Calculate the number of joules released when 72.5 grams of water at 95.0 °C cools to a final temperature of28.0 °C.q = m × c × △Tq = 72.5 g × 4.184 Jg °C × (28.0 °C − 95.0 °C)q = −20323.78 JThe water releases 20,300 joulesof energy. The negative sign shows release.How does enthalpy change during phase changes?For matter to transition from one state to another, a certain amount of energy transfer is needed to overcome (or succumb to) the intermolecular attractions. This is why the temperature of a substance does not increase during phase changes. The direction of energy flow determines the sign of the enthalpy value.Phase ChangeEnthalpy TypeDeposition,condensation, freezingExothermic (−△H or −q)Sublimation,vaporization, meltingEndothermic (+△H or +q)FQ: How is the heat of reaction calculated for a chemical reaction?What is the heat of reaction?During a chemical reaction, energy is absorbed and is used for the breaking of bonds in the reactants. Simultaneously, bonds are being formed to create products and energy is released. However, these individual energy exchanges do not determine whether a reaction is endothermic or exothermic. We need to know the overall change in enthalpy. This is determined by comparing the sum of the enthalpies of the reactants to the sum of the enthalpies of the products. This comparison will help you determine the overall change in enthalpy, also known as theheat of reaction.the change in the enthalpy of a chemical reaction that occurs at a constant pressureDownloaded by Ronin Steven (roninsteven9@gmail.com)lOMoARcPSD|46891182
What is the equation to calculate the heat ofreaction?△H = Hproducts− HreactantsThe heat of reaction (overall change in enthalpy) is found by taking the sum of enthalpies of the products and subtracting the sum of enthalpies of the reactants.What is the total enthalpy change of a reaction?How does △H become positive or negative? Well, breaking bonds in molecules in the reactants absorbs energy, and forming new bonds between atoms in the products releases energy. The amount of energy absorbed or released depends on the types of bonds.The total enthalpy change in a reaction is a combination of the energy usedto break bonds in the reactants (activation energy) and the energy released when bonds are formed in the products (energy difference between the transition state, or the peak in a potential energy diagram, and the sum of theenthalpies of the products).How does △H become positive or negative?EndothermicExothermicEndothermicIf the amount of energy required to break bonds in the reactants is more than the amount of energy released in forming bonds in the products, the chemicalreaction is endothermic and +△H.ExothermicIf the amount of energy required to break bonds in the reactants is less than the amount of energy released in forming bonds in the products, the chemicalreaction is exothermic and −△H.How can enthalpy change be used as aconversion factor todetermine heat of reaction?The enthalpy change of a reaction or process is usually expressed in kilojoules per mole (kJ/mol) in a thermochemical equation (a balanced chemical equation that shows the enthalpy change in a reaction).This means enthalpy change can be used as a conversion factor to determine the heat of reaction when a certain amount of reactants is used. Remember to use thevirtual periodic tableto determine the molar mass, in g/mol, of a compound.The chemical reaction and enthalpy change forburning methane (CH4) is given below. If 38.5 grams of methane are burned, how The enthalpy change value of this reaction tells us that for every mole of methane (CH4) burned, 890.0 kilojoules are given off because the enthalpy change is negative. This is an exothermic reaction. Use the enthalpy change as a conversion factor between moles of methane and kilojoules of energy.38.5 g CH4 ÷ 1× 1 mol CH4 ÷ 16.05 g CH4× −890.0 kJ ÷ 1 mol CH4= −2,135kJDownloaded by Ronin Steven (roninsteven9@gmail.com)lOMoARcPSD|46891182
many kilojoules of energy are transferred, and is this reaction endothermic or exothermic? CH4+ O2→ CO2+ 2H2O△H = −890.0 kJ/molThis shows that as 38.5 grams of methane are burned, 2,140 kilojoulesof energy are released.During an endothermic reaction, H for the reactants was −200 kJ/mol. What rangeof values could the H for the products be for this reaction?Recall, for endothermic reactions, the change in enthalpy is positive. This means the △H > 0.You are also told that the Hreactants= −200 kJ/mol. With this information, we can write:Hproducts− Hreactants> 0Hproducts− (−200 kJ/mol) > 0Hproducts> −200 kJ/molSo, any value where Hproductsis greater than −200 kJ/mol would give an endothermic reaction. In an endothermic reaction, the amount of energy required to break bonds in the reactants is more than the amount of energy released in forming bonds in the products.The combustion of isooctane fuel (C8H18) has an enthalpy change of −5,460 kJ/mol. How many kilojoules of energyare released when 350.0 grams of isooctane are burned?(negative means released!!!)Be sure to record any extra helpful notes, vocabulary terms, and practice sample problems.Downloaded by Ronin Steven (roninsteven9@gmail.com)lOMoARcPSD|46891182