level 1
What are the reactants in the equation 2H₂ + O₂ → 2H₂O?
a) H₂O and O₂
b) H₂ and O₂
c) H₂ and H₂O
d) O₂ and H₂O
Answer: b) H₂ and O₂
Which of the following is an example of a chemical reaction?
a) Melting ice
b) Burning wood
c) Cutting paper
d) Dissolving sugar in water
Answer: b) Burning wood
What do chemical equations represent?
a) The physical state of matter
b) The rearrangement of atoms in a chemical reaction
c) The temperature of a substance
d) The shape of molecules
Answer: b) The rearrangement of atoms in a chemical reaction
If the equation C + O₂ → CO₂ is balanced, how many carbon atoms are on each side?
a) 1
b) 2
c) 3
d) 4
Answer: a) 1
Which of these is a physical change?
a) Burning paper
b) Melting ice
c) Rusting iron
d) Baking a cake
Answer: b) Melting ice
What do subscripts in chemical formulas tell us?
a) How many molecules there are
b) How many atoms of an element are present
c) The total mass of a molecule
d) The temperature of the reaction
Answer: b) How many atoms of an element are present
What do coefficients in a chemical equation indicate?
a) The speed of the reaction
b) The number of molecules or atoms involved
c) The temperature of the reaction
d) The type of reaction
Answer: b) The number of molecules or atoms involved
In the chemical formula H₂SO₄, how many sulfur atoms are present?
a) 1
b) 2
c) 3
d) 4
Answer: a) 1
In the reaction CH₄ + 2O₂ → CO₂ + 2H₂O, how many oxygen atoms are on the product side?
a) 2
b) 4
c) 6
d) 8
Answer: b) 4
In the formula 3H₂O, what does the coefficient "3" represent?
a) 3 oxygen atoms
b) 3 molecules of water
c) 3 hydrogen atoms
d) 3 molecules of hydrogen ga
Answer: b) 3 molecules of water
What is the product in the equation Na + Cl₂ → NaCl?
a) Sodium
b) Chlorine
c) Sodium chloride
d) Chloride
Answer: c) Sodium chloride
In the reaction 2H₂ + O₂ → 2H₂O, how many oxygen atoms are in the products?
a) 1
b) 2
c) 4
d) 6
Answer: b) 2
Which of the following must be balanced in a chemical equation?
a) The number of molecules
b) The number of atoms for each element
c) The speed of the reaction
d) The weight of the products
Answer: b) The number of atoms for each element
What happens when a chemical equation is balanced?
a) The atoms on each side are equal
b) The products weigh more
c) Energy is lost
d) Matter is created
Answer: a) The atoms on each side are equal
What must happen to bonds in a chemical reaction?
a) Bonds must break and reform
b) Bonds must be destroyed
c) Bonds must stay the same
d) No changes occur in bonds
Answer: a) Bonds must break and reform
How many hydrogen atoms are in the formula 2H₂O?
a) 1
b) 2
c) 4
d) 6
Answer: c) 4
Which is a sign that a chemical reaction has occurred?
a) Change in color
b) Water freezing
c) Glass breaking
d) Water evaporating
Answer: a) Change in color
What is the reactant in the following equation: 2Na + Cl₂ → 2NaCl?
a) NaCl
b) Sodium
c) Chloride
d) Both b and c
Answer: d) Both b and c
Which law is used to balance chemical equations?
a) Law of gravity
b) Law of conservation of mass
c) Law of thermodynamics
d) Law of conservation of energy
Answer: b) Law of conservation of mass
The equation 2H₂ + O₂ → 2H₂O represents what type of reaction?
a) Physical change
b) Chemical reaction
c) No change
d) Energy release only
Answer: b) Chemical reaction
What does the law of conservation of mass state?
a) Energy is created during a reaction
b) Matter is destroyed during a reaction
c) Mass is conserved in both reactants and products
d) Mass is only conserved in physical changes
Answer: c) Mass is conserved in both reactants and products
.How many oxygen atoms are in the chemical formula CO₂?
a) 1
b) 2
c) 3
d) 4
Answer: b) 2
What is the role of a subscript in a chemical formula?
a) It shows the total mass of the molecule
b) It indicates the number of atoms of each element
c) It tells how fast the reaction happens
d) It changes the reactants
Answer: b) It indicates the number of atoms of each element
What is formed during a chemical reaction?
a) New substances
b) Physical changes
c) Energy
d) No changes occur
Answer: a) New substances
Which is an example of a chemical formula?
a) NaCl
b) H₂O
c) CO₂
d) All of the above
Answer: d) All of the above