Notes
Equations and conservation of mass
- Reactants (left) turn into products (right). Coefficients show amounts; subscripts are never changed when balancing.
- Mass is conserved: the total mass of reactants equals the total mass of products, and each type of atom has the same count on both sides.
Balancing and reaction types
- Balance by adjusting coefficients: $\text{2H}_2 + \text{O}_2 \rightarrow \text{2H}_2\text{O}$.
- Types: synthesis ($\text{A} + \text{B} \rightarrow \text{AB}$), decomposition, single replacement, double replacement, combustion.
Energy and rates
- Exothermic reactions release energy; endothermic reactions absorb it. Activation energy is needed to start a reaction.
- Rates increase with higher temperature, higher concentration, greater surface area and a catalyst.
Topics in this unit
Each topic has its own short notes and practice.
Practice
Only this one has 2 N and 6 H on both sides.
$10 - 5.6 = 4.4$ g.
One element replaces another in a compound.
Endothermic reactions absorb energy from the surroundings.
Cooling slows particle motion and collisions.
Right side has $2 \times 3 = 6$ O atoms, so 3 $\text{O}_2$.
Free response
Write your answer first, then open the scoring guide.
Free-response question
Methane burns in oxygen: $\text{CH}_4 + \_\text{O}_2 \rightarrow \text{CO}_2 + \_\text{H}_2\text{O}$.
(a) Balance the equation.
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$\text{CH}_4 + \text{2O}_2 \rightarrow \text{CO}_2 + \text{2H}_2\text{O}$
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(b) If 16 g of methane burns with 64 g of oxygen, what is the total mass of the products?
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Mass is conserved, so the products have a mass of $16 + 64 = 80$ g.
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(c) Classify the reaction by type and by energy change, and give one way to make it go faster.
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It is a combustion reaction and is exothermic (releases heat). It would go faster with a higher temperature, more concentrated oxygen, or a greater surface area of the fuel.
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