Together that is where we get the +1 overall on NH 4 +. In NH 4 +, each hydrogen has an oxidation number of +1 while nitrogen still has an oxidation number of -3. Once again, the oxidation number of hydrogen is +1 when it is combined with a nonmetal. In our reactants we have protonation of ammonia so we’re looking at NH 4 +. In uncharged NH 3, each hydrogen has an oxidation number of +1 while nitrogen then has an oxidation number of -3. We can look at nitrogen in our reactants and products.įirst our products: The oxidation number of hydrogen is +1 when it is combined with a nonmetal as in CH 4, NH 3, H 2O, and HCl. The number is the effective charge on an atom in a compound. The oxidation number describes explicitly the degree to which an element can be oxidized (lose electrons) or reduced (gain electrons). Specifically, we want to hone in on nitrogen. We can stick with answer choice C as our correct answer.ģ) This is another passage-based question in this set, but once again, the test-maker simplifies our lives a bit by telling us where we will find the necessary information to answer our question. × This answer choice incorrectly includes the solid reactant and product instead of excluding these.This is going to be our best answer choice. This answer choice matches our breakdown.Pure solids and liquids are not included when writing out our equilibrium constant. We noted in our equation that limestone (CaCO 3) is a solid.We noted in our equation that CaO is a solid.That means we are only left with the product CO 2 (g). That means we are not including CaCO 3 (s) and CaO (s) from our initial equation. Pure solids and liquids are not included when writing out this equilibrium constant. However, before we write anything for this specific question, what we need to pay attention to is the state of each reactant and product. If we have an equation aA + bB ⇌ cC + dD, we can write out the equilibrium constant expression: Each concentration is raised to the power of its coefficient in the balanced chemical equation. The equilibrium constant is the ratio of the mathematical product of the concentrations of the products of a reaction to the mathematical product of the concentrations of the reactants of the reaction. We’re told an equilibrium is established and we can write out the equation here: We’re asked about limestone being heated during Step 1. We can stick with answer choice B as our best answer choice.Ģ) This question has to do with the same part of the passage we focused on for Question 1. We expect ΔG to be positive and greater than TΔS. This answer choice is the opposite of what we said in our breakdown. Given our equation ΔG = ΔH – TΔS, ΔH must be greater than TΔS in order for ΔG to be positive. Entropy increases going from a solid reactant to gas in our products, so we have a positive ΔS. For nonspontaneous reactions, ΔG is positive. We mentioned some key points in the breakdown that we can reiterate here. This answer choice is entirely consistent with our breakdown of the question. That means this answer choice is only half right. Given our equation ΔG = ΔH – TΔS, ΔH must be positive and greater than TΔS in order for ΔG to be positive. Entropy increases if we go from a solid reactant to a gas in our products, so we have a positive ΔS, and we’re told temperature is 900 K. We mentioned that for nonspontaneous reactions, ΔG is positive. First part of this answer choice is consistent with our breakdown. Given this information, ΔG can only be positive in our above equation when ΔH is positive and is greater than TΔS (which we know is also a positive number in this circumstance). Additionally, entropy increases if we go from a solid reactant to a gas in our products, which would mean a positive ΔS. We don’t get the decomposition the author talks about in Step 1, and for nonspontaneous reactions, ΔG is positive. Let’s jump into some quick background information we’ll use to answer this question: What does that tell us? The reaction is not spontaneous. The limestone, CaCO 3( s) is only heated to 900 K, but does not decompose and generate CO 2( g) and CaO( s). The author tells us in Step 1, “The chemist placed a sample of limestone, CaCO 3( s), into a sealed chamber and then heated the limestone to 1200 K to generate CO 2( g) and CaO( s).” However, there’s a slight change in the question stem. 1) First thing we want to do to answer this question is revisit the part of the passage that talks about limestone.
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