Reaction calculations
Đã giới thiệu| English | Ý nghĩa |
|---|---|
| mole ratio/məʊl ˈreɪʃɪəʊ/ | tỷ lệ mol |
| yields/jiːldz/ | hiệu suất |
Predicting how much you get
- A balanced equation is a recipe: it tells you exactly how much product a reaction makes.
- Reaction calculations use moles to work this out.
Balance the equation
Step the coefficients until every element has the same number of atoms on both sides.
Reaction calculation route
Follow a known mass through a balanced equation to the answer.
How many moles are in 4 g of hydrogen gas (Mr = 2)?
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moles = 4 ÷ 2 = 2.
The big numbers in a balanced equation give the ______ ratio.
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Reactions combine in whole-number mole ratios.
The mole ratio 摩尔比
- The big numbers in a balanced equation give the mole ratio of reactants and products.
- In 2H₂ + O₂ → 2H₂O, 2 moles of hydrogen make 2 moles of water.
A titration measures exactly how much acid reacts with a base
In 2H₂ + O₂ → 2H₂O, the mole ratio of H₂ to H₂O is:
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
2 moles of H₂ give 2 moles of water.
Put the reaction-calculation steps in order.
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Mass → moles → ratio → moles → mass.
The method
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- Find the moles of the substance you know (mass ÷ Mr).
-
- Use the mole ratio to find moles of the substance you want.
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- Convert back to mass (moles × Mr) if needed.
Worked example. How much water from 4 g of hydrogen (Mr = 2) burning in oxygen? Moles of H₂ = 4 ÷ 2 = 2. The ratio H₂ : H₂O is 2 : 2, so 2 moles of water form. Mass = 2 × 18 = 36 g.
If 2 moles of water form (Mr of water = 18), what mass of water is that?
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
mass = 2 × 18 = 36 g.
Why it matters
- These calculations let chemists and factories work out yields 产率 and amounts needed.
- They avoid waste and predict exactly how much product to expect.
Use the mole ratio, not the mass ratio. Reactions combine in whole-number ratios of moles, not grams. Always convert mass to moles before applying the ratio from the equation.
You've got it
- the balanced equation gives the mole ratio of reactants to products
- method: mass → moles → (ratio) → moles → mass
- always work in moles, not masses, when using the ratio
Write from 88 grams of carbon dioxide
- Calcium carbonate decomposes as CaCO3 to CaO plus CO2.
- Two moles of calcium carbonate react. Mr of CO2 is 44. Two moles of water in the lesson have mass 36 g.
What mass of carbon dioxide forms?
Two moles of CO2 have mass 88 g.
What mass of CO2 comes from two moles of calcium carbonate?
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
The equation gives one mole of CO2 per mole of carbonate.