Why chemistry works with other sciences
Chemistry is the science of matter and how it changes. Today almost every big problem needs chemistry plus another subject.
- Chemistry + biology: designing medicines that fit a body target.
- Chemistry + physics: solar cells and batteries that move charge.
- Chemistry + engineering: making a lab reaction work in a huge tank.
- Chemistry + computing: computers help predict which new molecule will work.
This mixing of subjects is called interdisciplinary work.
Making new molecules: synthesis and catalysis
Synthesis means building a wanted molecule from simpler ones. Chemists plan steps so that each step gives a good amount of product and little waste.
Most reactions need a push of energy to start. This push is the activation energy. A catalyst gives the reaction an easier path, so the hill is lower. The catalyst is not used up and the final products are the same. Examples: iron in making ammonia, enzymes in your body, and platinum-group metals in a car exhaust converter.
A catalyst speeds up a reaction. It does not change how much product is possible in the end.
New materials and energy chemistry
Chemists design materials by choosing atoms and how they are joined: light strong plastics, thin screens, and materials that store energy.
In a rechargeable lithium-ion battery, lithium ions (Li⁺) move through a liquid between two electrodes. Charging pushes ions into one electrode. Using the battery lets them move back, and the electrons go through the wire and power your device.
Other energy chemistry: fuel cells (make electricity from hydrogen and oxygen, with water as the product) and solar materials.
Process engineering: from flask to plant
Chemical engineering turns a lab reaction into a safe, cheap, big process. A plant has a reactor (where the reaction happens), a separator (which splits product from leftovers) and pipes that can carry the leftovers back. This is recycling of unreacted feed.
Say one pass through the reactor converts 40 % of the feed. With no recycle, 60 % is wasted. With full recycle of the leftover, nearly all of it is finally turned into product.
Engineers also think about heat, safety, cost and waste. Aiming for less waste is called green chemistry.
Try it
Put a little hydrogen peroxide (ask an adult, use the 3 % pharmacy kind) in two cups. Add a pinch of dry yeast to one. Watch the bubbles: the yeast has enzymes, which are natural catalysts. Predict first, then check. Always wear safety glasses.
Key formulas and definitions
- Activation energy = energy of the hill top − energy of the reactants
- Catalyst: lowers activation energy; not used up; same products
- Overall conversion with full recycle ≈ 100 % of the feed (in theory)
- Percent conversion per pass = (feed converted ÷ feed in) × 100
Worked examples
1. A reaction needs 80 kJ to start. A catalyst lowers the hill to 50 kJ. By how much did the hill fall?
80 − 50 = 30 kJ. The catalyst gave an easier path; the products are still the same.
2. A reactor converts 40 % of the feed in one pass. If 100 kg enters, how much is converted and how much is left?
Converted = 0.40 × 100 = 40 kg. Left = 60 kg. With a separator and recycle, this 60 kg goes back in.
3. Which of these is NOT used up in a reaction: reactant, product or catalyst?
The catalyst. Reactants are used up and products are formed; the catalyst comes out unchanged.
Common mistakes
- Thinking a catalyst is a reactant that gets used up. It comes out unchanged.
- Thinking a catalyst changes the final amount of product. It only changes the speed.
- Thinking recycle means reusing the product. It means sending unreacted feed back.
- Thinking chemistry only happens in a lab. Batteries, medicines and plants are all chemistry at work.