CHEMISTRY HIGH SCHOOL

50 POINTS Which of the following is a synthesis reaction?

2H2O yields 2H2 + O2

H2 + Cl2 yields 2HCl

2Li + CaO yields Li2O + Ca

CH4 + 2O2 yields CO2 + 2H2O

Answers

Answer 1
Answer: You will notice that the first answer decomposes into two seperate products with 1 reactant, so since this is only true of decomposition reactions, that is not the answer.

H2+Cl2 yields 2HCl could be the answer, as it starts with 2 reactants and ends with one product, something found in synthesis reactions. 

The third answer is incorrect because even though there are no decompositions of single products, the metal exchanges positions, something that only occurs in decomposition reactions.

In the fourth answer is also incorrect because the methane is oxidized. This only happens in decomposition reactions.

The correct answer, then, is B.

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2. What mass of sodium chloride is produced when chlorine gas reacts with 2.29 grams of sodium iodide? The unbalanced equation is given below: Nal (s) + Cl, (g) → NaCl (s) + 1, (g)​

Answers

Answer:

0.88g

Explanation:

The reaction equation:

         2NaI  + Cl₂   →    2NaCl  + I₂

Given parameters:

Mass of Sodium iodide = 2.29g

Unknown:

Mass of NaCl = ?

Solution:

To solve this problem, we work from the known to the unknown.

First find the number of NaI from the mass given;

   Number of moles  = (mass)/(molar mass)  

          Molar mass of NaI  = 23 + 126.9  = 149.9g/mol

 Now insert the parameters and solve;

     Number of moles  = (2.29)/(149.9)   = 0.015mol

So;

 From the balanced reaction equation;

            2 moles of NaI produced 2 moles of NaCl

          0.015mole of NaI will produce 0.015mole of NaCl

Therefore;

      Mass  = number of moles x molar mass

      Molar mass of NaCl = 23 + 35.5  = 58.5g/mol

Now;

      Mass of NaCl  = 0.015 x 58.5  = 0.88g

A mixture consists of sand and an aqueous saltsolution. Which procedure can be used to separate
the sand, salt, and water from each other?
(1) Evaporate the water, then filter out the salt.
(2) Evaporate the water, then filter out the sand.
(3) Filter out the salt, then evaporate the water.
(4) Filter out the sand, then evaporate the water.

Answers

Answer is (4).

Explanation:

The given mixture contains an insoluble solid and an aqueous solution of salt.  The insoluble solid is sand. 

First we have to separate insoluble solid. Sand can be separated by doing filtration. When we filter the mixture sand can be seen as the residue on the filter paper. 

After filtering the mixture, we should collect the filtrate. Filtrate is the salt solution. By doing evaporation we can get the solid salt. 

First and second choices are wrong because after evaporating water filtrationcannot be done and salt and sand will be mixed together.

Salt cannot befiltered out because the salt is soluble and it is inaqueous medium. Hence, third choice is wrong
the best answer is 4  because if you get rid of the sand first and evaporate the water you're left with salt

What are the half equations that exist in thus reaction: 4Na + O2 --->2Na2O .

Answers

4Na +2e- ---->2Na2
O2 +2e- ------>2O

Bromine has two isotopes 79Br and 81Br, whose masses (78.9183 and 80.9163 amu) and abundances (50.69% and 49.31%, respectively) were determined in earlier experiments. Calculate the average atomic mass of bromine based on these experiments.

Answers

Answer:

Average atomic mass = 79.9034 amu

Explanation:

The formula for the calculation of the average atomic mass is:

Average\ atomic\ mass=(\frac {\%\ of\ the\ first\ isotope}{100}* {Mass\ of\ the\ first\ isotope})+(\frac {\%\ of\ the\ second\ isotope}{100}* {Mass\ of\ the\ second\ isotope})

Given that:

For first isotope:

% = 50.69 %

Mass = 78.9183 amu

For second isotope:

% = 49.31 %

Mass = 80.9163 amu

Thus,  

Average\ atomic\ mass=(50.69)/(100)* {78.9183}+(49.31)/(100)* {80.9163}\ amu

Average\ atomic\ mass=40.0036+39.8998\ amu

Average atomic mass = 79.9034 amu

Is rubber band stretching physical or chemical

Answers

Answer:

\boxed {\boxed {\sf Physical \ change}}

Explanation:

A chemical change, as the name suggests, must result from a change in the chemical makeup and new substances are produced. A very common example is metal rusting.

A physical change can be observed without a change in chemical composition. No new substances are produces. Ripping paper and an ice cube melting are physical changes.

A rubber band stretching is a physical change. No new substances are made and the chemical makeup remains the same.

Answer:

physical

Explanation:

this is a physical action to create a change. does not involve chemicals or elements

How did Niels Bohr describe electrons in his atomic model?

Answers

Neils Bohr proposed that an electron is found only in specific circular paths or orbits around the nucleus. Each orbit has a fixed energy and are called energy levels. The nearest electron to the nucleus has the lowest energy level and the farthest is the strongest energy level. The energy of an electron is said to be quantized.

Neils Bohr described that :They orbit the central nucleus in discrete paths.
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