Question

class set - do not write on test!!!!
midterm: chemistry 2025 - 2026 chemical equations and reactions
version b

1. how many total atoms of oxygen are present in the reactants? ( 6co_2 + 6h_2o \to c_6h_{12}o_6 + 6o_2 )

a) 6 c) 18
b) 12 d) 24

1. which of the following sets of coefficients will balance the reaction below?

__ ( fe + ) ( o2 \to )__ ( fe_2o_3 )
a) 2, 3, 4 c) 4, 3, 2
b) 1, 2, 3 d) 2, 3, 1

Explanation:

Step1: Count oxygen atoms in \(CO_2\)

In \(6CO_2\), each \(CO_2\) has 2 oxygen atoms. So \(6\times2 = 12\) oxygen atoms from \(CO_2\).

Step2: Count oxygen atoms in \(H_2O\)

In \(6H_2O\), each \(H_2O\) has 1 oxygen atom. So \(6\times1=6\) oxygen atoms from \(H_2O\).

Step3: Sum up oxygen atoms

Total oxygen atoms in reactants: \(12 + 6=18\)

for question 11:

Step1: Balance oxygen atoms

Let the coefficients be \(aFe + bO_2
ightarrow cFe_2O_3\). For oxygen: \(2b = 3c\). Try \(c = 2\), then \(b=3\).

Step2: Balance iron atoms

For iron: \(a = 2c\). Since \(c = 2\), \(a = 4\)

Answer:

C. 18