Which of the following equations shows a chemical change?(1 point)
Responses
NH3(g)→NH3(l)
N H 3, which is a gas right-arrow N H 3, which is a liquid
H2O(s)→H2O(g)
H 2 O, which is a solid right-arrow H 2 O, which is a gas
C2H5OH(l)→C2H5OH(g)
C 2 H 5 O H, which is a liquid right-arrow C 2 H 5 O H, which is a gas
C3H8+5O2→3CO2+4H2O
C3H8+5O2→3CO2+4H2O
The equation that shows a chemical change is C3H8 + 5O2 → 3CO2 + 4H2O.
The equation that shows a chemical change is the last one: C3H8+5O2→3CO2+4H2O.
To determine if a chemical change has occurred, you need to look for evidence of a chemical reaction. In this equation, you can see that C3H8 (propane) reacts with oxygen (O2) to produce carbon dioxide (CO2) and water (H2O). The reactants (C3H8 and O2) are transformed into the products (CO2 and H2O), indicating a chemical change.
The other equations given involve phase changes (changes in state of matter) rather than chemical reactions. NH3(g) → NH3(l) shows the change from a gas to a liquid (condensation). H2O(s) → H2O(g) represents the change from a solid to a gas (sublimation). C2H5OH(l) → C2H5OH(g) shows the change from a liquid to a gas (evaporation). These phase changes do not involve the formation of new substances and, therefore, do not represent a chemical change.
How many atoms of carbon (C) are present in the reactants of the following chemical equation?
C7H16+O2→CO2+H2O
(1 point)
Responses
7 atoms
7 atoms
16 atoms
16 atoms
23 atoms
23 atoms
1 atom
There are 7 atoms of carbon (C) present in the reactants of the chemical equation.
In the reactant C7H16 (heptane), there are 7 carbon atoms.
Use the equation to answer the question.
CH4 + 2O2 → CO2 + 2H2O
If you change the 2 in front of 2O2
to a 3, what will be the change in the results on the right side of the equation?
(1 point)
Responses
There is an extra O2
molecule left over.
There is an extra cap o sub 2 molecule left over.
Nothing changes in the equation.
Nothing changes in the equation.
There are now 3H2O
molecules.
There are now 3 cap h sub 2 cap o molecules.
There are now 3CO2
molecules.
If you change the 2 in front of 2O2 to a 3, the change in the results on the right side of the equation is that there are now 3CO2 molecules.
According to the Law of Conservation of Mass, if 88 g of carbon dioxide ( CO2
) is produced in a reaction between oxygen (O) and 24 g of carbon (C), what is the mass of dioxygen ( O2
) in the reactants?(1 point)
Responses
24 g
24 g
32 g
32 g
104 g
104 g
64 g
64 g
To determine the mass of dioxygen (O2) in the reactants, we can use the balanced chemical equation and the Law of Conservation of Mass.
The balanced equation is:
C + O2 → CO2
From the equation, we can see that for every 1 mole of carbon (C), we need 1 mole of O2 to produce 1 mole of CO2.
The molar mass of CO2 is 44 g/mol.
So, to produce 88 g of CO2, we need 88 g/44 g/mol = 2 moles of CO2.
Since we need an equal amount of O2 to produce CO2, we also need 2 moles of O2.
The molar mass of O2 is 32 g/mol.
Therefore, the mass of O2 in the reactants is 2 moles * 32 g/mol = 64 g.
The correct answer is 64 g.
One molecule of bromine (Br2) and two molecules of potassium chloride (KCl) combine in a reaction. How many atoms are in the products?(1 point)
Responses
four
four
six
six
three
three
two