Question

QUESTION 1
In the reaction C7H16 + ------- O2 → 8H2O + 7CO2, what coefficient should be placed in front of O2 to balance the reaction?
A. 7
B. 8
C. 11
D. No coefficient is needed
QUESTION 2
In the reaction -------- H2 + O2 → 2H2O, what coefficient should be placed in front of H2 to balance the reaction?
A. 1
B. 2
C. 3
D. No coefficient is needed
QUESTION 3
How does the law of conservation of mass apply to this reaction: C2H4 + 3O2 → 2H2O + 2CO2?
A. The equation needs to be balanced. There are fewer oxygen atoms in the equation than hydrogen or carbon.
B. Only the oxygen needs to be balanced. There are equal numbers of hydrogen and carbon.
C. The law of conservation of mass has already been applied. There is an equal number of each element on both sides of the equation.
D. Each element needs to be balanced.
QUESTION 4
How does the law of conservation of mass apply to this reaction: Mg + HCI → H2 + MgCI2?
A. The equation needs to be balanced. There are fewer hydrogen atoms in the equation than magnesium or chlorine.
B. Only the hydrogen needs to be balanced. There are equal numbers of magnesium and chlorine.
C. The law of conservation of mass has already been applied. There is an equal number of each element on both sides of the equation.
D. Hydrogen and chlorine need to be balanced. There is an equal amount of magnesium on each side.

Answer 1

So,

1. Simply count the oxygen atoms in the products.

$8H_2O*\frac{1\ O atom}{1H_2O}=8\ O\ atoms\\7CO_2*\frac{2\ O atom}{1CO_2}=14\ O\ atoms$

There are 22 O atoms in the products.  Therefore, we should put a coefficient of 11 in front of the $O_2$ in order to have 22 O atoms in the reactants.

The correct answer is C.

2. Using the same conversions as in the first question, you can see that there are 2*2 = 4 H atoms in the products.  Therefore, a coefficient of 2 must be placed in front of the $H_2$ to have 4 H atoms in the reactants.

The correct answer is B.

3. Check to see if there are equal numbers of each atom on both sides.

There are 2 C's on the left and 2 C's on the right.  There are 4 H's on the left and 4 H's on the right.  There are 6 O's on the left and 6 O's on the right (from both water and carbon dioxide).  Therefore, the equation is balanced.

The correct answer is C.

4. Do the same thing as in the previous question.  There is 1 Mg on both sides, but there is only 1 H and 1 Cl on the left and 2 of each on the right.  Thus, the correct answer is D.

Answer 2

Answer:

For less confusion and stuff the answer is 10 or D

Explanation: