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Conner A.
Graduate Teaching Assistant
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Geology
TutorMe
Question:

Explain what gravity field anomalies are what information can be discerned from them.

Conner A.
Answer:

Gravity field anomalies are regions where gravity measurement corrections result in a gravity value that is positive or negative and thus deviate from zero, which represents the the determined gravity value based on a simplified model of the earths shape and average density. So the anomalies result from heterogeneity not accounted for in the model. A negative anomaly results from a gravity correction that subtracts too much, the true density is lower than the assumed density of the earth. A positive anomaly results from the true density being higher than the assumed density.

Chemistry
TutorMe
Question:

Often the following relationships are stated: Kw = Kb * Ka Kw = 1*10-14 at 25 degree C pH + POH = 14 Explain what if anything happens to the sum of pH + POH when the temperature is changed. Will the neutral pH of water remain the same?

Conner A.
Answer:

At different temperatures, the value of Kw, the auto-ionization constant of water, will not remain 1*10-14. It will increase or decrease like all equilibrium constants. Kw = Kb * Ka will still hold true, and thus the concentration of hydronium and hydroxide ions will thus change accordingly, because Kw = [H3O+][OH-] from the autoioniztion reaction of water. Due to the relationship pH = -log[H3O+], the neutral pH of water will no longer be equal to 7 (POH will also change accordingly) and the sum of pH + POH will no longer equal 14.

Basic Chemistry
TutorMe
Question:

Consider the following unbalanced chemical reaction: _ C4H10(g) + _ O2(g) --> _ CO2(g) + _ H2O(g) Determine the mass of Carbon Dioxide, CO2, produced by the reaction if 5 grams of Butane, C4H10, reacts with 20 moles of oxygen, O2.

Conner A.
Answer:

1) To answer this question, the reaction must first be balanced, that is the coefficient of each reactant and product must be determined first. To balance, first focus on either the carbon or hydrogen atoms present on each side of the reaction, as they are unique to each product and will thus be easiest to balance first. 1 C4H10(g) + _ O2(g) --> 4 CO2(g) + 5 H2O(g) Now the reaction has 4 carbon atoms (C) and 10 hydrogen atoms (H) on each side of the reaction. Now we can balance the oxygen atoms. Currently each side of the reaction has 2 & 13 atoms of oxygen respectively. Since 13 is an odd number and is not a multiple of 2, all the coefficients must be doubled so each side of the reaction has an even number of atoms of oxygen. 2 C4H10(g) + _ O2(g) --> 8 CO2(g) + 10 H2O(g) Now the reaction can be fully balanced for oxygen. There are 26 atoms of oxygen on the products side, so a coefficient of 13 must be placed in from of oxygen to balance the reaction. 2 C4H10(g) + 13 O2(g) --> 8 CO2(g) + 10 H2O(g) 2) Now that the chemical reaction is balanced, the amount of carbon dioxide produced by the reaction can be determined. To do this, the limiting reactant must be determined for the reaction, either butane or oxygen gas,. The limiting reactant will be the reactant that produces the smallest amount of product, basically it is the 'ingredient' in shortest supply. This can be found using stoichiometry. Butane: First the mass of butane available to react, 5 grams, must be converted to moles using butane's molar mass (mm = 58.12 g/mol) 5 g C4H10 * 1 mol / 58.12 g C4H10 = 0.086 mol C4H10 Now the moles of CO2 produced must be determined by converting from moles of butane to moles of carbon dioxide. This is done by multiplying by the mole ratio of products to reactants, determined from coefficients we determined earlier. In this case, for ever 8 moles of carbon dioxide produced, 2 moles of butane are consumed so the ratio is 8 mol CO2 / 2 mol C4H10. 0.086 mol C4H10 * (8 mol CO2 / 2 mol C4H10) = 0.344 mol CO2 Now the amount of CO2 that could be produced by oxygen must be determined. Oxygen is already in moles, so the first step of converting from grams to moles can be skipped. 20 mol O2 * (8 mol CO2 / 13 mol O2) = 12.3 mol CO2 The moles of CO2 produced by the given amount of oxygen is much greater than what could be produced by C4H10, so butane is the limiting reactant. Now all that needs to be done is to convert the moles of carbon dioxide produced by the limiting reactant to grams using the molar mass. 0.344 mol CO2 * 44.01 g/mol CO2 = 15.1 g of CO2

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