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Acetylene $\left(\mathrm{C}_{2} \mathrm{H}_{2}\right)$ can be made by reacting calcium carbide (CaC $_{2}$ ) with water. (a) Write an equation for the reaction. (b) What is the maximum amount of heat (in joules) that can be obtained from the combustion of acetylene, starting with $74.6 \mathrm{g}$ of $\mathrm{CaC}_{2} ?$

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$1.5 \times 10^{3} \mathrm{KJ}$

Chemistry 101

Chapter 6

Thermochemistry

University of Central Florida

Rice University

University of Kentucky

Lectures

05:27

In chemistry, a chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Both reactants and products are involved in the chemical reactions.

06:42

In chemistry, energy is what is required to bring about a chemical reaction. The total energy of a system is the sum of the potential energy of its constituent particles and the kinetic energy of these particles. Chemical energy, also called bond energy, is the potential energy stored in the chemical bonds of a substance. Chemical energy is released when a bond is broken during chemical reactions.

03:54

Acetylene $\left(\mathrm{C…

02:42

Acetylene gas, $\mathrm{C}…

04:29

for this problem has two parts and for part a were supposed to find the equation for when settling is produced when we react calcium carbide and water. So we know for sure, or to reacting for calcium, carbide and water. And we know that one of the products is unsettling, but we are missing a product, and the reason why we know that is because there's an oxygen here in the water. But there's no oxygen on the right side. So we need to find out what that missing product is and the way we can do that. Is we confined? How this reaction actually occurs. So we know that in this case, when water splits up, we can express it as hoh And we know that the calcium carbide splits into calcium in the carbon. And so for the settling here, we know that's formed in the calcium where, when the carbon bonds with hydrogen So then logically, the last product has to be when the calcium bond, the hydroxide ion. So we can just add that here calcium hydroxide and the last thing that we need to do is we need to balance his equation. So we look at the left side. We look at calcium. Calcium is balanced. One mole of calcium on both sides. We look at carbon. Carbon is also balanced. We have to on each side. Now we look at hydrogen. Hydrogen is unbalanced because we only have two on the left side. But we have four on the right. So we just added to correct for that. And that also fixes their oxygen problem because now we have two moles of oxygen atoms on both sides. So for part a, the final reaction can be return. Have such that is the final answer now for part B. Part B now asked us for how much he is released when some amount of settling is combusted, starting with 74.6 grams of C eight. See to the first thing that we need to do we need to actually write the combustion reaction for settling. We know that for combustion reactions for this one, we are starting with settling and then in combustion reactions. We always have oxygen as a reacting and you have liquid water and carbon dioxide as the products. Now we need to balance this. We first looked to the carbon two moles on the left side. Only one more on the right. We added to here to balance you. Look at the hydrogen. Hydrogen is balanced. We have two on the left to on the right now Oxygen. We have two on the left, but we have five on the right. So now we need to correct for that. And then we will correct. For that, we just add 5/2. But this does not work. And the reason why it doesn't work is because now we have a fraction as a coefficient to fix. For that, we just multiply everything by two. And then when you multiply everything by two, you will get the final combustion reaction tools of a settling five moles of oxygen, gas, two moles of liquid water and for most of carbon dioxide. So now we have the combustion reaction. Now we need to do is we need to find how much heat is released on these combustion reaction so that we can relate it finally to calcium carbide. Answer the question. So, as always, you can find the heat of the reaction by finding the heats, informations the products and then subtracting out the heats informations from the reactions you already know. We can disregard the auction because the heat's informations of all elements are zero. So we start on the products. We have two moles of water and we know that the heat of formation of water is negative. 285 0.8 kilograms per mole. We have four, most of carbon dioxide, and we know that the huge every formation for carbon dioxide is negative. 293.5 killed tools from all. And finally we subtract out the two moles of settling and the heat. Information for a settling is 200 and 26.6 kilograms promote. And when you put that all into calculator, you'll get the heat of this reaction. It's negative 2000 at 600 killer jewels promote. However, we need to row somehow relate this to calcium carbide because that is the quantity that given in the problem. So the first thing we need to do is we need to set up a proportion. So we know that 2000 and 600 killer jewels of heat are released, and they dropped the negative sign because released implies that it already takes that into account, and it knows that its next thermic reaction. And we know that for every 2600 coaches he released that two moles of a settling reacted as shown here on our equation. So we get two moles of C two h two, and we can relate that to calcium carbide because we did this in Part eight. We know that the mole ratio between calcium carbide and unsettling is 1 to 1. So we have one mole of it settling and one more of calcium carbide, and from there it's pretty straightforward. All we need to do is divide by the more math of calcium carbide, which happens to be 64 point 099 grams per mole and then finally multiplied by the initial quantity of your given, which is 74.6 grams of C A C two. And when you multiply all of that together, you will get that the amount of heat released or the heat obtained from this reaction is going to be 1000 500 cured jewels, and that is the final answer

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