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2 years ago

8

For which of the following activities might you want to hire a chemist?

2 answers:

worty [1.4K]2 years ago

7 0

For which of the following activities might you want to hire a chemist?

Answer: D. testing a rock sample for gold content

Which of the following procedures involves a physical change in one of the substances?

Answer: C. separating a salt solution by evaporating the water

Crank2 years ago

6 0

A. examining the structure of plant cells

Incorrect. A biologist is required.

B. building a fence

Incorrect. A carpenter is required.

C. building a wood storage shed

Incorrect. A carpenter is required.

D. testing a rock sample for gold content

Incorrect. A chemist is required.

A. creating salt by reacting sodium metal and chlorine gas

Incorrect. This is a chemical change as a new product is formed.

B. allowing a nail rust

Incorrect. This is a chemical change as it is the oxidation of iron to form iron oxide, rust.

C. separating a salt solution by evaporating the water

Correct. This is a physical change as salt gets separated from water and no new product is formed.

D. building a model rocket propelled by mixing baking soda and vinegar

Incorrect. This is a chemical change.

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Which statement best describes insoluble substances?

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Water does not remain when an insoluble substance is added

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What is the total energy change for the following reaction:CO+H2O-CO2+H2

Alekssandra [29.7K]

Answer:

$\large \boxed{\text{-41.2 kJ/mol}}$

Explanation:

Balanced equation: CO(g) + H₂O(g) ⟶ CO₂(g) + H₂(g)

We can calculate the enthalpy change of a reaction by using the enthalpies of formation of reactants and products

$\Delta_{\text{rxn}}H^{\circ} = \sum \left( \Delta_{\text{f}} H^{\circ} \text{products}\right) - \sum \left (\Delta_{\text{f}}H^{\circ} \text{reactants} \right)$

(a) Enthalpies of formation of reactants and products

$\begin{array}{cc}\textbf{Substance} & \textbf{$\Delta_{\text{f}}$H/(kJ/mol}) \\\text{CO(g)} & -110.5 \\\text{H$_{2}$O} & -241.8\\\text{CO$_{2}$(g)} & -393.5 \\\text{H$_{2}$(g)} & 0 \\\end{array}$

(b) Total enthalpies of reactants and products

$\begin{array}{ccr}\textbf{Substance} & \textbf{Contribution)/(kJ/mol})&\textbf{Sum} \\\text{CO(g)} & -110.5& -110.5 \\\text{H$_{2}$O(g)} &-241.8& -241.8\\\textbf{Total}&\textbf{for reactants} &\mathbf{ -352.3}\\&&\\\text{CO}_{2}(g) & -393.5&-393.5 \\\text{H}_{2} & 0 & 0\\\textbf{Total}&\textbf{for products} & \mathbf{-393.5}\end{array}$

(c) Enthalpy of reaction $\Delta_{\text{rxn}}H^{\circ} = \sum \left( \Delta_{\text{f}} H^{\circ} \text{products}\right) - \sum \left (\Delta_{\text{f}}H^{\circ} \text{reactants} \right)= \text{-393.5 kJ/mol - (-352.3 kJ/mol}\\= \text{-393.5 kJ/mol + 352.3 kJ/mol} = \textbf{-41.2 kJ/mol}\\ \text{The total enthalpy change is $\large \boxed{\textbf{-41.2 kJ/mol}}$}$

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2 years ago

Oxygen has an atomic number of 8. in order to fill its outer electron shell, how many electrons does it need?

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Oxygen has 8 electrons. On the outer ring, it has 6 valance electrons. It need 2 more valance electrons to be stable.

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3 years ago

Draw the Lewis structure for the Se and 2 H atoms.

fomenos

When drawing lewis dot diagram structure we consider the number of valence electrons of the atom.Se has six valence electrons since it is in group six thus it Lewis dot diagram is as follows
..
: Se:
Hydrogen is in group one hence has one valence electron.The lewis dot diagram for 2H is therefore
H:H

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