Concept explainers
Use standard enthalpies of formation to calculate
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Principles of Chemistry: A Molecular Approach (3rd Edition)
- A 0.470-g sample of magnesium reacts with 200 g dilute HCl in a coffee-cup calorimeter to form MgCl2(aq) and H2(g). The temperature increases by 10.9 C as the magnesium reacts. Assume that the mixture has the same specific heat as water and a mass of 200 g. (a) Calculate the enthalpy change for the reaction. Is the process exothermic or endothermic? (b) Write the chemical equation and evaluate H.arrow_forwardThe thermochemical equation for the burning of methane, the main component of natural gas, is CH4(g)+2O2(g)CO2(g)+2H2O(l)H=890kJ (a) Is this reaction endothermic or exothermic? (b) What quantities of reactants and products are assumed if H = 890 kJ? (c) What is the enthalpy change when 1.00 g methane burns in an excess of oxygen?arrow_forwardAssume 200. mL of 0.400 M HCl is mixed with 200. mL of 0.400 M NaOH in a coffee-cup calorimeter The temperature of the solutions before mixing was 25.10 C; after mixing and allowing the reaction to occur, the temperature is 27.78 C. What is the enthalpy change when one mole of acid is neutralized? (Assume that the densities of all solutions are 1.00 g/mL and their specific heat capacities are 4.20 J/g K.)arrow_forward
- Nitrogen monoxide, a gas recently found to be involved in a wide range of biological processes, reacts with oxygen to give brown NO2 gas. 2 NO(g) + O2(g) NO2(g)rH = 114.1 kJ/mol-rxn Is this reaction endothermic or exothermic? What is the enthalpy change if 1.25 g of NO is converted completely to NO2?arrow_forwardUse Appendix L to find the standard enthalpies of formation of oxygen atoms, oxygen molecules (O2), and ozone (O3). What is the standard state of oxygen? Is the formation of oxygen atoms from O2 exothermic? What is the enthalpy change for the formation of 1 mol of O3 from O2?arrow_forwardUse standard enthalpies of formation in Appendix L to calculate enthalpy changes for the following: (a) 0.054 g of sulfur burns, forming SO2(g) (b) 0.20 mol of HgO(s) decomposes to Hg() and O2(g) (c) 2.40 g of NH3(g) is formed from N2(g) and excess H2(g) (d) 1.05 102 mol of carbon is oxidized to CO2(g)arrow_forward
- What mass of acetylene, C2H2(g), must be burned to produce 3420 kJ of heat, given that its enthalpy of combustion is 1301 kJ/mol? Compare this with the answer to Exercise 5.91 and determine which substance produces more heat per gram.arrow_forwardUse Hesss law to calculate the enthalpy change for the formation of CS2() from C(s) and S(s) [C(s) + 2 S(s) CS2()] from the following enthalpy values. C(s)+O2(g)CO2(g)rH1=393.5kJ/mol-rxnS(s)+O2(g)SO2(g)rH2=296.8kJ/mol-rxnCS2(l)+3O2(g)CO2(g)+2SO2(g)rH3=1103.9kJ/mol-rxnarrow_forwardThe enthalpy changes for the following reactions can be measured: CH4(g) + 2 O2(g) CO2(g) + 2 H2O(g) rH = 802.4 kJ/mol-rxn CH3OH(g) + 32 O2(g) CO2(g) + 2 H2O(g) rH = 676 kJ/mol-rxn (a) Use these values and Hesss law to determine the enthalpy change for the reaction CH4(g) + O2(g) CH3OH(g) (b) Draw an energy level diagram that shows the relationship between the energy quantities involved in this problem.arrow_forward
- 9.41 Under what conditions does the enthalpy change equal the heat of a process?arrow_forwardChloroform, CHCl3, is formed from methane and chlorine in the following reaction. CH4(g) + 3 Cl2(g) 3 HCl(g) + CHCl3(g) Calculate rH, the enthalpy change for this reaction, using the enthalpies of formation of CO2(g), H2O(), CHCI3(g) (fH = 103.1 kJ/mol), and the enthalpy changes for the following reactions: CH4(g) + 2 O2(g) 2 H2O() + CO2(g) rH = 890.4 kJ/mol-rxn 2 HCl(g) H2(g) + Cl2(g) rH = +184.6 kJ/mol-ransarrow_forward
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