Category 1
What is a balanced chemical equation? Why should a chemical equation be balanced?
A balanced chemical equation is one where the number of atoms of each element in the reactant side is equal to the number of atoms of each element in the product side.
A chemical equation must be balanced to satisfy the law of conservation of mass which states that mass can neither be created nor be destroyed in a chemical reaction.
A student conducts a reaction between 5.0 g of A and 5.0 g of B in an open beaker. After the reaction, the total mass of the products in the beaker is 8.5 g. Does this violate the Law of Conservation of Mass?
a. Yes, because the mass decreased from 10g to 8.5g.
b. Yes, because the chemical properties of the substance changed.
c. No, because mass is only conserved in closed systems and not in open ones.
d. No, because a gaseous product likely escaped into the atmosphere.
d. No, because a gaseous product likely escaped into the atmosphere.
A student performs the reaction between lead nitrate and potassium iodide using hot solutions but does not see any precipitate. When the solution is cooled, a yellow precipitate appears.
Lead iodide is soluble in hot water but insoluble in cold water. Hence, no precipitate forms initially, but on cooling, PbI₂ precipitates.
CASE STUDY: In the process of photosynthesis, plants convert carbon dioxide and water into glucose and oxygen: CO2 + H2O -----> C6H12O6 + O2. If a plant consumes 6 molecules of CO2, how many molecules of H2O are required to keep the equation balanced?
a. 6
b. 12
c. 1
d. 3
a. 6
Which coefficient set balances the following complex reaction:
aKMnO4 + bHCl -----> cKCl + dMnCl2 + eH2O + fCl2?
1. a=1 b=8 c=1 d=1 e= 4 f=2.5
2. a=1 b=4 c=1 d=1 e= 2 f=1
3. a=2 b=16 c=2 d=2 e= 8 f=5
4. a=2 b=8 c=2 d=2 e= 4 f=3
3. a=2 b=16 c=2 d=2 e= 8 f=5