1answer.
Ask question
Login Signup
Ask question
All categories
  • English
  • Mathematics
  • Social Studies
  • Business
  • History
  • Health
  • Geography
  • Biology
  • Physics
  • Chemistry
  • Computers and Technology
  • Arts
  • World Languages
  • Spanish
  • French
  • German
  • Advanced Placement (AP)
  • SAT
  • Medicine
  • Law
  • Engineering
artcher [175]
3 years ago
5

Which of the following is not an indication of a chemical reaction?

Chemistry
2 answers:
lakkis [162]3 years ago
8 0
A substance freezes.  
Y_Kistochka [10]3 years ago
3 0

Answer:

A substance freezes

Explanation:

Two substances bursting into flames on contact can be seen as a combustion reaction, and this usually happens with very volatile substances, and is a chemical reaction that changes the substance on the atomic level.

A substance freezing simply demonstrates a phase change, and does not alter the molecule on any level, apart from the arrangement of the atoms.

Bubbles forming when two substances are combined is the indication that a gas has been formed as a product. The only way a gas can be formed is by a chemical change, usually oxygen or hydrogen is given off.

A solid forming is usually named a precipitation reaction, and the solid is called a precipitate, and this is a chemical reaction that forms an insoluble substance.

You might be interested in
i am begging anyone to help me with this! (all tutors i've asked said they can't solve it but i need someone to help me out) - i
9966 [12]

First, we need to calculate how much energy we will get from this combustion.

Assuming the combustion is complete, we have the octane reacting with O₂ to form only water and CO₂, so:

C_8H_{18}+O_2\to CO_2+H_2O

We need to balance the reaction. Carbon only appear on two parts, so, we can start by it:

C_8H_{18}+O_2\to8CO_2+H_2O

Now, we balance the hydrogen:

C_8H_{18}+O_2\to8CO_2+9H_2O

And in the end, the oxygen:

C_8H_{18}+\frac{25}{2}O_2\to8CO_2+9H_2O

We can multiply all coefficients by 2 to get integer ones:

2C_8H_{18}+25O_2\to16CO_2+18H_2O

Now, we need to use the enthalpies of formation to get the enthalpy of reaction of this reaction.

The enthalpy of reaction can be calculated by adding the enthalpies of formation of the products multiplied by their stoichiometric coefficients and substracting the sum of enthalpies of formation of the reactants multiplied by their stoichiometric coefficients.

For the reactants, we have (the enthalpy of formation of pure compounds is zero, which is the case for O₂):

\begin{gathered} \Delta H\mleft\lbrace reactants\mright\rbrace=2\cdot\Delta H\mleft\lbrace C_8H_{18}\mright\rbrace+25\cdot\Delta H\mleft\lbrace O_2\mright\rbrace \\ \Delta H\lbrace reactants\rbrace=2\cdot(-250.1kJ)+25\cdot0kJ \\ \Delta H\lbrace reactants\rbrace=-500.2kJ+0kJ \\ \Delta H\lbrace reactants\rbrace=-500.2kJ \end{gathered}

For the products, we have:

\begin{gathered} \Delta H_{}\mleft\lbrace product\mright\rbrace=16\cdot\Delta H\lbrace CO_2\rbrace+18\cdot\Delta H\lbrace H_2O\rbrace \\ \Delta H_{}\lbrace product\rbrace=16\cdot(-393.5kJ)+18\cdot(-285.5kJ) \\ \Delta H_{}\lbrace product\rbrace=-6296kJ-5139kJ \\ \Delta H_{}\lbrace product\rbrace=-11435kJ \end{gathered}

Now, we substract the rectants from the produtcs:

\begin{gathered} \Delta H_r=\Delta H_{}\lbrace product\rbrace-\Delta H\lbrace reactants\rbrace \\ \Delta H_r=-11435kJ-(-500.2kJ) \\ \Delta H_r=-10934.8kJ \end{gathered}

Now, this enthalpy of reaction is for 2 moles of C₈H₁₈, so for 1 mol of C₈H₁₈ we have half this value:

\Delta H_c=\frac{1}{2}\Delta H_r=\frac{1}{2}\cdot(-10934.8kJ)=-5467.4kJ

Now, we have 100 g of C₈H₁₈, and its molar weight is approximately 114.22852 g/mol, so the number of moles in 100 g of C₈H₁₈ is:

\begin{gathered} M_{C_8H_{18}}=\frac{m_{C_8H_{18}}}{n_{C_8H_{18}}} \\ n_{C_8H_{18}}=\frac{m_{C_8H_{18}}}{M_{C_8H_{18}}}=\frac{100g}{114.22852g/mol}\approx0.875438mol \end{gathered}

Since we have approximately 0.875438 mol, and 1 mol releases -5467.4kJ when combusted, we have:

Q=-5467.4kJ/mol\cdot0.875438mol\approx-4786.37kJ

Now, for the other part, we need to calculate how much heat it is necessary to melt a mass, <em>m</em>.

First, we have to heat the ice to 0 °C, so:

\begin{gathered} Q_1=m\cdot2.010J/g.\degree C\cdot(0-(-10))\degree C \\ Q_1=m\cdot2.010J/g\cdot10 \\ Q_1=m\cdot20.10J/g \end{gathered}

Then, we need to melt all this mass, so we use the latent heat now:

Q_2=n\cdot6.03kJ/mol

Converting mass to number of moles of water we have:

\begin{gathered} M=\frac{m}{n} \\ n=\frac{m}{M}=\frac{m}{18.01528g/mol} \end{gathered}

So:

Q_2=\frac{m}{18.01528g/mol}_{}\cdot6.03kJ/mol\approx m\cdot0.334716kJ/g

Adding them, we have a total heat of:

\begin{gathered} Q_T=m\cdot20.10J/g+m\cdot0.334716kJ/g \\ Q_T=m\cdot0.02010kJ/g+m\cdot0.334716kJ/g \\ Q_T=m\cdot0.354816kJ/g \end{gathered}

Since we have a heat of 4786.37 kJ form the combustion, we input that to get the mass (the negative sign is removed because it only means that the heat is released from the reaction, but now it is absorbed by the ice):

\begin{gathered} 4786.37kJ=m\cdot0.354816kJ/g \\ m=\frac{4786.37kJ}{0.354816kJ/g}\approx13489g\approx13.5\operatorname{kg} \end{gathered}

Since we have a total of 20kg of ice, we can clculate the percent using it:

P=\frac{13.5\operatorname{kg}}{20\operatorname{kg}}=0.675=67.5\%

5 0
1 year ago
The sum of protons and neutrons in an atom is called the.
tresset_1 [31]
Atomic mass / mass number / atomic weight

(all of which mean the same thing)
6 0
2 years ago
Sodium carbonate (NaCO3) is sometimes used as a water-softening agent. Suppose that a worker prepares a 0.730 M solution of NaCO
sergey [27]

The molarity of a solution is the number of moles of a substance divided by the volume in liters prepared.

molarity=\frac{n}{V}, where n is number of moles and V is the volume in liters.

In order to calculate the mass of solute we need to convert the volume and molarity to moles

1.421 L solution \times\frac{0.0730 moles}{1 Lsolution}= 1.037 mol NaCO_3

Now that we have moles we use the relative formula mass of NaCO₃, We have 1 Na atom, 1 C atom and 3 O atoms, thus

M_r= (1\times 22.99) + (1\times 12.00) + (3\times 16.00)= 82.99g/mol

1.037 \times\frac{82.99g}{mol} = 86.1g

5 0
3 years ago
Read 2 more answers
Which type of energy uses the photoelectric effect?
ikadub [295]

Answer:

My lovely people the answer is SOLAR

Explanation:

i just know

8 0
2 years ago
Which type of energy in the bungee cord prevents the bungee jumper from hitting the ground
Effectus [21]
Elastic potential energy
7 0
3 years ago
Other questions:
  • A chemistry student needs of 65 gr acetyl bromide for an experiment. She has available 20 g of 38.1 % a w/w solution of acetyl b
    7·1 answer
  • How many formula units are in 9.039 moles of sodium chloride
    9·1 answer
  • Determine the frequency of radiation whose wavelength is 7.67 x 10^-7 cm. Then, determine the amount of energy in the radiation.
    8·1 answer
  • Zoom in if need to<br> PLEASE HELP DUE TOMARROW
    5·1 answer
  • If you have 30.O g of hydrogen gas burned in excess oxygen how many moles of water can you make
    11·1 answer
  • calculate the speed of an electron if its de broglie wavelength is twice its displacement in one second
    15·1 answer
  • The atomic mass of carbon-13 is 13. It has six protons. How many neutrons does this isotope have?
    15·2 answers
  • Calculate the theoretical yield for the amount of sodium carbonate produced as a result of this chemical reaction. Record your f
    6·1 answer
  • Which pair shares the same empirical formula? (
    14·1 answer
  • Four groups of students were each asked to create table listing two elements and two compounds. Only one group’s table was corre
    6·1 answer
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!