Term 1 review: reactions, electricity and heredity
الأسبوع 15 · مراجعة الفصل الدراسي الأول (الوحدات ١–٤) ومهام مراجعة من إعداد Darslab · 3 دروس
1
Review: reactions, combustion and smoking
Science Prep 3 Term 1, Units 1–4: Review
GoalReview reactions, combustion and smoking by solving new mixed tasks. No new facts.
New words
balanced equation · an equation with the same number of each kind of atom on both sidescombustion · a reaction of a substance with oxygen that gives off energyaddiction · a strong need to keep doing something even when it harms you
Explanation
Remember the ideas. In every reaction the atoms are kept and only rearranged, so the mass before equals the mass after and the equation must balance. A more reactive metal can take the place of a less reactive one. Combustion needs fuel, oxygen and a start (the fire triangle). Complete combustion of a hydrocarbon gives carbon dioxide and water; with too little oxygen it can give carbon monoxide, which is dangerous. Remove one side of the triangle to put a fire out. Smoking harms the lungs and heart, and addiction makes it hard to stop; asking for help is a strength. Now use these ideas in the new tasks below.
2Mg + O2,2MgO
atoms: 2 Mg and 2 O on each side
Worked examples
Balance: Fe + O₂ → Fe₂O₃. Try 4Fe + 3O₂ → 2Fe₂O₃: left 4 Fe and 6 O; right 4 Fe and 6 O. Balanced.
Mass: 24 g of magnesium burns with 16 g of oxygen. The oxide has a mass of 24 + 16 = 40 g, so the mass is conserved.
A small pan fire: cover it with a lid (a grown-up does it) to remove the oxygen. Never pour water on a fat fire. If anything is unsafe, leave and call an adult.
Class activity
Review mat. Draw the fire triangle and write one way to remove each side safely. Then write: one equation to balance (Fe + O₂ → Fe₂O₃), one reason why a more reactive metal displaces a less reactive one (use the reactivity series list) and one kind sentence for a friend who wants to stop smoking.
Practice
1
Balance H₂ + O₂ → H₂O.
2H₂ + O₂ → 2H₂O.
2
Name the three sides of the fire triangle.
Fuel, oxygen, and a start (heat).
3
Why is carbon monoxide dangerous?
It is a poisonous gas that stops the blood from carrying oxygen well.
4
In a reaction 10 g of A and 6 g of B give a single product. What is its mass?
