The methane molecule, CH4, has the geometry shown in Figure. Imagine a hypothetical process in which the methane molecule is “expanded,” by simultaneously extending all four C—H bonds to infinity. We then have the process CH4(g) → C(g) + 4 H(g)
Propose a reason for why two Styrofoam® cups are often used instead of just one.
Figure Coffee-cup calorimeter. This simple apparatus is used to measure temperature changes of reactions at constant pressure.
(a) Compare this process with the reverse of the reaction that represents the standard enthalpy of formation of CH4(g). (b) Calculate the enthalpy change in each case. Which is the more endothermic process? What accounts for the difference in ΔH° values? (c) Suppose that 3.45 g CH4(g) reacts with 1.22 g F2(g), forming CH4(g) and HF(g) as sole products. What is the limiting reagent in this reaction? If the reaction occurs at constant pressure, what amount of heat is evolved?
Examen 10, 11 Review preterite Tener: tuve, tuviste, ío, tuvimos, tuvisteis, tuvieron Morir: morí, moriste,urío, morimos, moristeis,urieron Haber: hube, hubiste, hubo, hubimos, hubisteis, hubieron Preterite vs. Imperfect Imperfect is used ● To describe an ongoing past action ● To express habitual past actions or incomplete actions ● To describe physical and emotional states in the past ● Telling time (or age) in the past Ayer Clara fue (preterite) a casa de sus primsaludó (preterite) a su tcomió con ellos. Mientras Carlosleía (imperfect) las traducciones, Blantraducía (imperfect) otros textos. La niña tení (imperfect) ocho años era (imperfect) inteligente y alegre. Preterite (or “perfect tense”) is used for concrete past actions, to narrate a series of past actions or events, and to express the beginning or the end of a past action. Like present progressive tense, there is a past progressive tense which uses estar in imperfect. I am eating tomatoes. Estoy comiendo tomates. VS. I was eating tomatoes. Estaba comiendo tomates. *** Notice only the tense of estar has changed. “Comiendo” remains the same. Another example is “Estoy estudiando para mi examen,” (I am studying for my exam) but if you were talking about the past, you might say “Estaba estudiando para mi examen” (I was studying for my exam). Imperfect has three irregular verbs… only three! IR, SER, and VER Yo iba Nosotros ibamos Tu ibas Vosotros ibais El/Ella/Ud. iba Ellos/Ellas/Uds. iban Yo era Nosotros eramos Tu eras Vosotros erais El/Ella/Ud. era Ellos/Ellas/Uds. eran Yo veÍa Nosotros veÍamos Tu veÍas Vosotros veÍais El/Ella/Ud. veÍa Ellos/Ellas/Uds. veÍan Otherwise, all verbs follow the same AR or IR/ER pattern. AR verbs aba abamos abas abais aba aban ER/IR verbs Ía Íamos Ías Íais Ía Ían Me dolÍan los pies. My feet were hurting. HabÍan un médico. There was a doctor. Cuando tenÍa 5 años me gustaba pizza. When I was 5 years old I liked pizza. Using both preterite and imperfect……………….. Ayer temprano por la mañana hubo un trágico accidente en el centro de Lima, cuando un autobús chocó con un carro. La mujer que manejaba el carro murió al instante. Los paramédicos llevaron al conductor del autobús al hospital porque tenía varias fracturas. Su estado de salud es todavía muy grave. El conductor del autobús dijo que no vio el carro hasta el último momento porque había mucha niebla y llovía. Vocabulary These chapters the vocabulary focuses on adverb use (mente), cars, technology and health. Doublecheck you’re comfortable with labeling a figure of a body (arm, leg, nose, mouth, ear, et cetera) Also familiarize yourself with verbs used in a doctor’s office (to get sick, to hurt, to prescribe, to be allergic, to cough, to sprain) Finally, know “las partes del carro” (breaks, tires, motor) and the vocabulary related to computers like homepage, internet, screen, files, and to print. Adverbs describe how an action is done (the how, when and where). Examples are bien, muy, mal, siempre, and nunca. You can form adverbs from adjectives by simply adding mente to the feminine form. Lento…..lentamente Feliz…...felizmente Fabuloso….fabulosamente Gordo….gordamente Aha! Trick. This is not a word. Other adverbs have to do with time ● A menudo (often) ● A tiempo (on time) ● A veces (sometimes) ● Muchas veces (a lot; many times) ● Pronto (soon) Culture Fácil! Read pages 288 and 289 about cyber cafes. 1. They are much more popular in South America than in the U.S. 2. They sometimes specialize in things like videogames 3. STudents can go to los cibercafes and do homework Por y para Por and para both mean “for” in English but they arot interchangeable. Uses for por Object of a search Exchange or substitution Duration of an action General location Unit of measure Uses for para Purpose Used with an infinitive Employment Deadline or specific time in the future Destination 1. Camino por la playa. 2. Camino para la playa. The first sentence is talking about the beach as a general location. “I walk by the beach” The second one, however, is talking about the beach as a destination “I walk towards the beach” *** Por/para can mean so much more than “for” making this a difficult concept to grasp