Chemistry, 23.10.2019 00:20 bikerhomie

Draw a cooling graph of water as it passes from 20°c to –20°c

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The graph will begin at 20 °C and have temperature on the y-axis and time on the x-axis. The line will be a downwards sloping one, until the value of temperature of the graph reaches 0 °C. There, it will become horizontal for a small amount of time, and then continue to slope downwards until the graph reaches -20 °C.

The horizontal region is where the freezing of water will take place, and there is no temperature change that occurs when a state change is taking place. This is because the energy involved then is latent energy.

Answer from: Quest

assuming that your periodic table has eighteen columns, you should highlight the four elements in the third column from the left of the table.

explanation

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the $3d$ have energy higher than those in the $4 s$ orbital while lower than those of the $4 p$ orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the $4s$ orbital is therefore filled right after $3p$ orbitals and before $3 d$ orbitals.

potassium has electron configuration $[\text{ar}] 4 s^{1}$ and calcium $[\text{ar}] 4 s^{2}$ . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration $[\text{ar}] 4 s^{2} \; 3d^{1}$ and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the $ns^{2} \; (n-1) p^{1}$ and should be highlighted as well.

Answer from: Quest

Both models are effective because they show the valence electrons, and these valence electrons indicate the reactivity of an element.

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Draw a cooling graph of water as it passes from 20°c to –20°c...