Heat of Formation Table for Common Compounds

The molar heat of formation  (also called standard enthalpy of formation) of a compound (ΔHf) is equal to its enthalpy change (ΔH) when one mole of compound is formed at 25 °C and 1 atm from elements in their stable form. You need to know the heat of formation values to calculate enthalpy and for other thermochemistry problems. This is a table of the heats of formation for a variety of common compounds. As you can see, most heats of formation are negative quantities, which implies that the formation of a compound from its elements usually is an exothermic process. Table of Heats of Formation Compound Hf (kJ/mol) Compound Hf (kJ/mol) AgBr(s) -99.5 C2H2(g) +226.7 AgCl(s) -127.0 C2H4(g) +52.3 AgI(s) -62.4 C2H6(g) -84.7 Ag2O(s) -30.6 C3H8(g) -103.8 Ag2S(s) -31.8 n-C4H10(g) -124.7 Al2O3(s) -1669.8 n-C5H12(l) -173.1 BaCl2(s) -860.1 C2H5OH(l) -277.6 BaCO3(s) -1218.8 CoO(s) -239.3 BaO(s) -558.1 Cr2O3(s) -1128.4 BaSO4(s) -1465.2 CuO(s) -155.2 CaCl2(s) -795.0 Cu2O(s) -166.7 CaCO3 -1207.0 CuS(s) -48.5 CaO(s) -635.5 CuSO4(s) -769.9 Ca(OH)2(s) -986.6 Fe2O3(s) -822.2 CaSO4(s) -1432.7 Fe3O4(s) -1120.9 CCl4(l) -139.5 HBr(g) -36.2 CH4(g) -74.8 HCl(g) -92.3 CHCl3(l) -131.8 HF(g) -268.6 CH3OH(l) -238.6 HI(g) +25.9 CO(g) -110.5 HNO3(l) -173.2 CO2(g) -393.5 H2O(g) -241.8 H2O(l) -285.8 NH4Cl(s) -315.4 H2O2(l) -187.6 NH4NO3(s) -365.1 H2S(g) -20.1 NO(g) +90.4 H2SO4(l) -811.3 NO2(g) +33.9 HgO(s) -90.7 NiO(s) -244.3 HgS(s) -58.2 PbBr2(s) -277.0 KBr(s) -392.2 PbCl2(s) -359.2 KCl(s) -435.9 PbO(s) -217.9 KClO3(s) -391.4 PbO2(s) -276.6 KF(s) -562.6 Pb3O4(s) -734.7 MgCl2(s) -641.8 PCl3(g) -306.4 MgCO3(s) -1113 PCl5(g) -398.9 MgO(s) -601.8 SiO2(s) -859.4 Mg(OH)2(s) -924.7 SnCl2(s) -349.8 MgSO4(s) -1278.2 SnCl4(l) -545.2 MnO(s) -384.9 SnO(s) -286.2 MnO2(s) -519.7 SnO2(s) -580.7 NaCl(s) -411.0 SO2(g) -296.1 NaF(s) -569.0 So3(g) -395.2 NaOH(s) -426.7 ZnO(s) -348.0 NH3(g) -46.2 ZnS(s) -202.9 Reference: Masterton, Slowinski, Stanitski, Chemical Principles, CBS College Publishing, 1983. Points To Remember for Enthalpy Calculations When using this heat of formation table for enthalpy calculations, remember the following: Calculate the change in enthalpy for a reaction using the heat of formation values of the  reactants  and  products.The enthalpy of an element in its standard state is zero. However, allotropes of an element not in the standard state typically do have enthalpy values. For example, the enthalpy values of O2 is zero, but there are values for singlet oxygen and ozone. The enthalpy of solid aluminum, beryllium, gold, and copper are zero. The vapor phases of these metal have enthalpy values.When you reverse the direction of a chemical reaction, the magnitude of ΔH is the same, but the sign changes.When you multiply a balanced equation for a chemical reaction by an integer value, the value of  ÃŽâ€H for that reaction must be multiplied by the integer, too. Sample Heat of Formation Problem For example, heat of formation values are used to find the heat of reaction for acetylene combustion: 2C2H2(g) 5O2(g) → 4CO2(g) 2H2O(g) 1) Check to make sure the equation is balanced. Youll be unable to calculate enthalpy change if the equation isnt balanced. If youre unable to get a correct answer to a problem, its a good idea to check the equation. There are many free online equation balancing programs that can check your work. 2) Use standard heats of formation for the products: ΔH ºf  CO2   -393.5 kJ/mole ΔH ºf  H2O -241.8 kJ/mole 3) Multiply these values by the stoichiometric coefficient. In this case, the value is 4 for carbon dioxide and 2 for water, based on the numbers of moles in the balanced equation: vpΔH ºf  CO2   4 mol (-393.5 kJ/mole) -1574 kJ vpΔH ºf  H2O 2 mol ( -241.8 kJ/mole) -483.6 kJ 4) Add the values to get the sum of the products. Sum of products (ÃŽ £ vpΔH ºf(products)) (-1574 kJ) (-483.6 kJ) -2057.6 kJ 5) Find enthalpies of the reactants. As with the products, use the standard heat of formation values from the table, multiply each by the stoichiometric  coefficient, and add them together to get the sum of the reactants. ΔH ºf  C2H2   227 kJ/mole vpΔH ºf  C2H2   2 mol (227 kJ/mole) 454 kJ ΔH ºf  O2   0.00 kJ/mole vpΔH ºf  O2   5 mol ( 0.00 kJ/mole) 0.00 kJ Sum of reactants (Δ vrΔH ºf(reactants)) (454 kJ) (0.00 kJ) 454 kJ 6) Calculate the heat of reaction by plugging the values into the formula: ΔH º Δ vpΔH ºf(products) - vrΔH ºf(reactants) ΔH º -2057.6 kJ - 454 kJ ΔH º -2511.6 kJ Finally, check the number of significant digits in your answer.

Classroom Behavior Essay - 1462 Words

Would you be surprised to learn that in today’s classroom children sometimes aren’t learning due to behavioral issues? Teachers are attempting to teach classes in which students can be disruptive, disrespectful and defiant. Classrooms are often overcrowded which adds to the frustration of the situation. Teachers are often tempted to take the easy way out, using antiquated strategies that will usually not help the child to learn. In fact, some types of punishments can actually cause the child to become even more rebellious. The child can experience a sense of worthlessness after being punished again and again. Children do not act out because they are â€Å"bad.† They act out in the hopes of receiving some kind of response or reward. In the†¦show more content†¦On the other hand, if that child fills the need for attention by getting into trouble at school, they will get into trouble. Skinner tells us that â€Å"non-reinforcement leads to the extinction of a behavior.† In other words if teachers figure out what the child is getting from exhibiting a particular behavior, they can then give that child the exact opposite of the expected response. If our response is consistent the child will eventually give up the behavior in lieu of another which yields more satisfying results. The reward system is sometimes turned around to reinforce poor behavior. Often, children who are misbehaving are looking for some sort of a reaction. It is possible that they believe that it is better to not even try than to try and fail. It could also be true that the only type of attention they r eceive comes from the instances in which they misbehave. 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Summer assignment free essay sample

Economics is a way of looking at the world and making rational decisions based on costs and benefits. Wondering how Over the summer, please read the book, Naked Economics: Undressing the Dismal Science, by Charles Wheelan. As you read the book, take notes that will help you answer some important questions and understand economic concepts. Your task is described below. Choose any five concepts discussed and analyzed by Wheelan. (The concepts should be from different chapters in the book.) Understanding the examples used in the book, try to relate these concepts to other situations that you might have experienced, or read about in the business/economic news. Create a poster, collage or a scrapbook related to your 5 economic events. Be ready to discuss your work in class. As you read the book, make a list of all the Nobel Prize winners mentioned. Be creative and have fun with the assignment. This assignment is due the first day of class. Enjoy your summer! AP Microeconomics Summer Assignment Economics is a way of looking at the world and making rational decisions based on costs and benefits. Wondering how Over the summer, please read the book, Naked Economics: Undressing the Dismal Science, by Charles Wheelan. As you read the book, take notes that will help you answer some important questions and understand economic concepts. Your task is described below. Choose any five concepts discussed and analyzed by Wheelan. (The concepts should be from different chapters in the book.) Understanding the examples used in the book, try to relate these concepts to other situations that you might have experienced, or read about in the business/economic news. Create a poster, collage or a scrapbook related to your 5 economic events. Be ready to discuss your work in class. As you read the book, make a list of all the Nobel Prize winners mentioned. Be creative and have fun with the assignment. This assignment is due the first day of class. Enjoy your summer! AP Microeconomics Summer Assignment Economics is a way of looking at the world and making rational decisions based on costs and benefits. Wondering how Over the summer, please read the book, Naked Economics: Undressing the Dismal Science, by Charles Wheelan. As you read the book, take notes that will help you answer some important questions and understand economic concepts. Your task is described below. Choose any five concepts discussed and analyzed by Wheelan. (The concepts should be from different chapters in the book.) Understanding the examples used in the book, try to relate these concepts to other situations that you might have experienced, or read about in the business/economic news. Create a poster, collage or a scrapbook related to your 5 economic events. Be ready to discuss your work in class. As you read the book, make a list of all the Nobel Prize winners mentioned. Be creative and have fun with the assignment. This assignment is due the first day of class. Enjoy your summer! AP Microeconomics Summer Assignment  Economics is a way of looking at the world and making rational decisions based on costs and benefits. Wondering how Over the summer, please read the book, Naked Economics: Undressing the Dismal Science, by Charles Wheelan. As you read the book, take notes that will help you answer some important questions and understand economic concepts. Your task is described below. Choose any five concepts discussed and analyzed by Wheelan. (The concepts should be from different chapters in the book.) Understanding the examples used in the book, try to relate these concepts to other situations that you might have experienced, or read about in the business/economic news. Create a poster, collage or a scrapbook related to your 5 economic events. Be ready to discuss your work in class. As you read the book, make a list of all the Nobel Prize winners mentioned. Be creative and have fun with the assignment. This assignment is due the first day of class. Enjoy your summer! AP Microeconomics Summer Assignment Economics is a way of looking at the world and making rational decisions based on costs and benefits. Wondering how Over the summer, please read the book, Naked Economics: Undressing the Dismal Science, by Charles Wheelan. As you read the book, take notes that will help you answer some important questions and understand economic concepts. Your task is described below. Choose any five concepts discussed and analyzed by Wheelan. (The concepts should be from different chapters in the book.) Understanding the examples used in the book, try to relate these concepts to other situations that you might have experienced, or read about in the business/economic news. Create a poster, collage or a scrapbook related to your 5 economic events. Be ready to discuss your work in class. As you read the book, make a list of all the Nobel Prize winners mentioned. Be creative and have fun with the assignment. This assignment is due the first day of class. Enjoy your summer! AP Microeconomics Summer Assignment Economics is a way of looking at the world and making rational decisions based on costs and benefits. Wondering how Over the summer, please read the book, Naked Economics: Undressing the Dismal Science, by Charles Wheelan. As you read the book, take notes that will help you answer some important questions and understand economic concepts. Your task is described below. Choose any five concepts discussed and analyzed by Wheelan. (The concepts should be from different chapters in the book.) Understanding the examples used in the book, try to relate these concepts to other situations that you might have experienced, or read about in the business/economic news. Create a poster, collage or a scrapbook related to your 5 economic events. Be ready to discuss your work in class. As you read the book, make a list of all the Nobel Prize winners mentioned. Be creative and have fun with the assignment. This assignment is due the first day of class. Enjoy your summer!

Why I Chose to Be an Engineer Essay Example For Students

Why I Chose to Be an Engineer Essay Science and especially more towards engineering has been my area of interest since my early years and I have always from that time loved to do experiments and observe chemicals in science. It is also one of the main reasons as to why I took up science during my high school. Since then I had participated debates, competitions related with science, shared and talked about my ideas clearly. I had also joined my schools science club where I learned the basics of doing research and how to prepare a science project like the baking soda volcano and making a boat sail in the water using rubber bands as an energy source. Throughout my childhood I have been exposed to a lot about or related to engineering, my grandfather was an Electrical Engineer and I used to spend a lot of time with him as a kid which got me interested in science in the first place, seeing my grandfather do all sorts of different things at home which seemed really interesting to me. We will write a custom essay on Why I Chose to Be an Engineer specifically for you for only $16.38 $13.9/page Order now My initial thoughts about engineering were that men in odd coloured clothes doing greasy, heavy labor work but as I grew up the thoughts changed for me completely and I got to know how amazing and interesting engineering actually is. As I started taking my science classes, I really started to enjoy the math, physics and chemistry and later I decided that I would take up engineering as a major because it seemed perfect for me. When I moved to the 11th grade, I came to know how broad and vast engineering actually is so I started to get to know about every field and was trying to decide what path I should take as I take up engineering so I talked with my friends about it, I talked to my parents and my grandfather and some help from the internet as well. Engineering seemed like the perfect major for me as I was willing to do the hard work, I loved the research and engineering seemed like the perfect major for me to use my skills and creativity. After doing some looking around and exploring I decided to take up mechanical engineering as my career path as I loved getting to know big machines, how they worked and broad the world for a mechanical engineer can be really got me interested but I also was really intrigued by the world of robotics and the advancements in it so with great backing from my father I decided to take up workshops and participate in competitions in robotics so that I can get to know more about them. That whole as an experience was great for me and it really helped me develop my knowledge in the field of engineering. By the time I was in my 12th grade I had already made for myself a simple career plan that I would do a Bachelor’s degree in Mechanical Engineering and then take up Mechatronics Engineering or Robotics and Automation for my Post-graduate studies. Engineering has been and still is making history and it has been the driving the evolution of the modern day and it is almost impossible to imagine a world without it now. Being a part of something that big and probably contributing to it is my dream.