Unit 5 · Segment 2: Matter Cycles and Energy Flows · printed p. 150 (PDF p. 186)
Chemical Reactions
Survival kits often include portable gear, such as hot packs and butane torches, that can be activated at a moment's notice.
Anchoring phenomenon
Chapters
- 12 Identifying Chemical Reactions
What evidence is enough to say that a new substance formed, and what evidence only looks like it?
1 presentation10 worksheets3 labs - 13 Atoms in Chemical Reactions
What happens to atoms during a chemical reaction, and why does the mass of a sealed system never change?
1 presentation10 worksheets3 labs - 14 Energy in Chemical Reactions
How does energy move between a chemical reaction and its surroundings, and how can engineers control that flow to build a useful device?
1 presentation10 worksheets3 labs - 15 Chemical Engineering and Society
Where do synthetic materials come from, why do people choose them over natural ones, and what do those choices cost?
1 presentation10 worksheets3 labs
Standards in this unit
Unit vocabulary
chemical reactionA change in which one or more substances turn into one or more different substances. The atoms are rearranged into new combinations, and the new substances have their own properties.Chapter 12
reactantA substance that is present before a chemical reaction and is changed by it.Chapter 12
productA substance that is made by a chemical reaction and was not there before it started.Chapter 12
physical changeA change in the size, shape, state or mixing of a substance that leaves it the same substance. Melting, boiling, crushing and dissolving are physical changes.Chapter 12
physical propertyA trait you can observe or measure without turning the substance into a different one, such as color, density, melting point, boiling point or solubility.Chapter 12
chemical propertyA description of whether and how a substance can change into new substances, such as whether it burns or whether it reacts with an acid. You can only find it out by letting the substance react or trying to make it react.Chapter 12
precipitateA solid that forms inside a liquid, usually when two dissolved substances react to make a substance that barely dissolves.Chapter 12
solubilityHow much of a substance can dissolve in a set amount of a liquid at a given temperature, often given in grams per liter of water.Chapter 12
melting pointThe temperature at which a solid turns into a liquid. A pure substance melts over a narrow range of about a degree or two; an impure sample starts melting lower and over a wider range.Chapter 12
indicator of reactionAn observable clue, such as a gas, a new color, a precipitate, a new smell, light or a temperature change, that suggests a reaction may have happened. Indicators are not proof; some physical changes show the same clues.Chapter 12
scientific evidenceObservations and measurements that back up or challenge a scientific claim.Chapter 12
clinical trialA planned study that tests a medicine in people to find out how well it works and what side effects it causes. Modern trials compare groups and are checked by an ethics board.Chapter 12
reactantA substance you start with in a chemical reaction. Its atoms are the only atoms the products can be built from. In an equation, reactants are written to the left of the arrow.Chapter 13
productA new substance formed by a chemical reaction, built from the regrouped atoms of the reactants. Products are written to the right of the arrow.Chapter 13
chemical equationA one-line record of a reaction using formulas: reactants, an arrow, products, with plus signs between substances. Read correctly, it is an inventory of atoms on each side.Chapter 13
coefficientThe whole number written in front of a formula that tells how many molecules or formula units of that substance take part. It multiplies every atom in the formula.Chapter 13
subscriptThe small number after an element symbol inside a formula that tells how many atoms of that element are in one molecule or formula unit. Changing a subscript changes the substance.Chapter 13
formula unitThe smallest repeating group of atoms in an extended structure, used for counting when a substance has no separate molecules. Fe₂O₃ is a formula unit of iron oxide, not a free-floating molecule.Chapter 13
law of conservation of matterThe scientific law that in any ordinary physical or chemical change, matter is neither created nor destroyed: each element keeps the same number of atoms, so the total mass after equals the total mass before.Chapter 13
scientific lawA statement, in words or math, of a pattern that has held in every careful test. A law describes what happens; a model or theory explains why.Chapter 13
closed systemA region, such as a sealed bag or capped container, that matter cannot enter or leave during the change you are studying. Energy such as heat or light can still cross the boundary.Chapter 13
open systemA region whose boundary matter can cross. In an open system, a balance reading can rise or fall during a reaction because atoms come in from the air or leave as gas, not because matter was made or destroyed.Chapter 13
catalystA substance that helps a reaction happen faster without being used up, so it can be recovered and used again instead of becoming waste.Chapter 13
atom economyThe percentage of the reactants' mass that ends up in wanted products rather than in waste, worked out from the balanced equations. Chemists use it to compare how efficient process designs are at using atoms.Chapter 13
systemThe matter you are following in a reaction: the reactants and the products they become, inside an imaginary boundary you draw so you can track energy crossing it.Chapter 14
surroundingsEverything outside the system that can exchange energy with it, such as the container, nearby air, water in a beaker, or the hand holding a pack.Chapter 14
exothermic reactionA reaction in which the system gives out more energy than it takes in, so the net flow of energy is out to the surroundings. The energy can leave as heat, light or sound.Chapter 14
endothermic reactionA reaction in which the system takes in more energy than it gives out, so the net flow of energy is in from the surroundings, which usually cool down. The word also describes other changes that absorb energy, such as some salts dissolving.Chapter 14
thermal energyThe energy a sample of matter has because its particles are moving. When thermal energy moves from a warmer object to a cooler one, that transfer is called heat.Chapter 14
temperatureA measure of how fast the particles in a sample are moving on average, read with a thermometer or probe. It is not the same as the amount of thermal energy, which also depends on how much matter there is.Chapter 14
chemical bondAn attraction that holds atoms together in a molecule or an extended structure. Pulling bonded atoms apart always takes energy in; forming a new bond always gives energy out.Chapter 14
net energy transferThe overall direction and size of the energy flow between a system and its surroundings after adding up everything absorbed and everything released.Chapter 14
prototypeA working version of a design that is built so it can be tested, with the results used to decide what to change in the next version.Chapter 14
criteriaThe measurable goals a design must meet to count as a success, such as a target temperature or a minimum working time.Chapter 14
constraintsThe limits a design must stay within, such as a budget, a safety ceiling, a maximum mass or the materials available.Chapter 14
iterationOne round of the build-test-modify cycle. Engineers repeat iterations, using the data from each round to choose the next change.Chapter 14
natural resourceA useful material that people take from Earth or from living things without chemically changing it into something new: ore dug from a mine, crude oil pumped from underground, nitrogen collected from the air, wood, cotton, hides or fish oil.Chapter 15
synthetic materialA material people produce from natural resources by chemical processes. 'Synthetic' describes how a material was made, not whether it is fake or harmful, and nature sometimes makes the same substance.Chapter 15
polymerA substance whose molecules are very long chains built from many repeating smaller units. Plastics, nylon, polyester, rubber and the cellulose in cotton are all polymers.Chapter 15
petroleumCrude oil, a liquid mixture of many carbon-and-hydrogen compounds that took millions of years to form from the buried remains of tiny ocean organisms. It is pumped from underground and separated at a refinery.Chapter 15
fossil fuelA natural resource that can be burned for energy and formed from the remains of organisms that lived long ago: coal, petroleum and natural gas. It is used far faster than Earth makes more.Chapter 15
renewable resourceA resource that nature replaces within a human lifetime, such as a crop harvested every year or leaves that regrow. Renewable does not mean unlimited; using it faster than it regrows still uses it up.Chapter 15
biofuelA fuel made from recently living material, such as ethanol fermented from the sugars in corn or oils pressed from algae, instead of from fossil fuels.Chapter 15
food additiveAny substance put into a food to change its flavor, color, texture, shelf life, nutrition or safety. Salt and sugar are natural additives; sucralose and Blue No. 1 are synthetic ones.Chapter 15
biodegradableAble to be broken apart into simpler substances by living things, mostly bacteria and fungi. How fast this happens depends on heat, moisture and oxygen, so a material can be biodegradable in a hot compost pile and last for years in a landfill.Chapter 15
criteriaThe things a design must do to count as a success, stated clearly enough to be tested: hold two kilograms, keep water out for ten minutes, break down within a year.Chapter 15
constraintA limit a design must stay within, such as a budget, the materials and tools on hand, a deadline or a law.Chapter 15
trade-offGiving up some of one benefit to gain more of another. Choosing a material almost always means accepting a cost to get a property you need.Chapter 15