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Questions in chemistry

[Free] For each pair of gases, select the one that most likely has the highest rate of effusion. Use the periodic table if necessary. Oxygen $(O_2)$ or hydrogen $(H_2)$ : $ Methane $(CH_4)$ or carbon tetrachloride $(CCl_4)$ : $ Nitrogen $(N_2)$ or ammonia $(NH_3)$ : $ Fluorine $(F_2)$ or chlorine $(Cl_2)$ : $

[Free] Draw a structural formula for the following: a. CH4 b. NaCl c. O₂ d. H₂O

[Free] A cube of iron ([tex]$C_p=0.450 J / g \cdot{ }^{\circ} C$[/tex]) with a mass of 55.8 g is heated from [tex]$25.0^{\circ} C$[/tex] to [tex]$49.0^{\circ} C$[/tex]. How much heat is required for this process? Round your answer to three significant figures. Use the formula [tex]$q=m C_p \Delta T$[/tex].

[Free] Two representative elements, nitrogen and oxygen, are in the same period of the periodic table. Which statement correctly describes the atoms of the two elements? A. They have the same number of valence electrons. B. They have valence electrons in different energy levels. C. They have the same number of electrons. D. They have valence electrons in the same energy level.

[Free] How many kPa are in $2,150 mmHg$?

[Free] This data set was created from examining several ice cores drilled at Antarctica's Vostok Station in 2001. Examine the data and write about one correlation that you see. What does the correlation tell you about Earth's historic atmosphere or climate? ($ybp =$ years before present, $ppb =$ parts per billion, and ppm = parts per million) | Depth (m) | Age (ybp) | Methane (ppb) | Carbon Dioxide (ppm) | Temperature Change from Current (${ }^{\circ} C$) | | --------- | --------- | ------------- | ------------------ | ------------------------------------------------- | | 355.765 | 9169 | 664.7 | 263 | 0.48 | | 362.915 | 9397 | 673.7 | 265.7 | 0.57 | | 374.57 | 9761 | 676.3 | 267.6 | 0.64 | | 381.715 | 9985 | 678 | 265.3 | 0.9 | | 389.97 | 10248 | 688 | 264 | 1.08 | | 399.215 | 10548 | 666 | 253.9 | 0.675 | | 407.43 | 10820 | 703 | 245.3 | 0.28 | | 415.27 | 11084 | 664.7 | 237.5 | -0.115 | | 427.27 | 11513 | 467.7 | 238.3 | -0.74 | | 434.52 | 11817 | 462.3 | 237.6 | -0.805 | | 445.965 | 12368 | 627 | 238.6 | -0.51 | | 453.77 | 12766 | 661.7 | 228.5 | -0.475 | | 463.565 | 13249 | 618.7 | 225.2 | -0.82 | | 469.72 | 13551 | 611.7 | 221 | -1.04 | | 484.02 | 14226 | 461 | 214 | -1.19 |

[Free] A chemist wants to calculate the amount of heat that is absorbed by a sample of copper as it is melted. Which constant should she use? A. [tex]$\Delta H_{\text {fus }}$[/tex] B. [tex]$-\Delta H_{\text {vap }}$[/tex] C. [tex]$\Delta H_{\text {vap }}$[/tex] D. [tex]$-\Delta H_{\text {fus }}$[/tex]

[Free] A sample of tin [tex]$\left( Cp =0.227 J / g \cdot{ }^{\circ} C \right)$[/tex] is placed in a freezer. Its temperature decreases from [tex]$15.0^{\circ} C$[/tex] to [tex]$-10.0^{\circ} C$[/tex] as it releases 543 J of energy. What is the mass of the sample? Round your answer to three significant figures. Use the formula [tex]$q=m C_\gamma \Delta T$[/tex].

[Free] Complete the table below using the drop-down menus. | Number of Protons | Number of Neutrons | Atomic Number | Mass Number | Element (symbol) | |---|---|---|---|---| | A | 7 | B | 15 | C | | D | E | 26 | 56 | F |

[Free] Name two elements that have a single valence electron.