Physical vs Chemical
Ice melting is an example of this type of change
What is a physical change?
The substances present at the beginning of a chemical reaction are called these and
The new substances produced during a chemical reaction are called these
Reactants and Products
A student mixes two clear liquids. The mixture becomes cloudy, its temperature increases and bubbles form.
Identify THREE pieces of evidence that suggest a chemical reaction has occurred
Temperature change, bubbles/gas production and formation of a new substance (the cloudy solid).
Together these provide strong evidence of a chemical change.
This chemical reaction occurs when wood, paper or fuel burns.
Bonus: give the word equation
What is combustion?
Fuel + Oxygen --> Carbon dioxide + Water + Energy (Heat and Light)
Why does crushing a solid reactant into smaller pieces generally make a reaction faster?
It increases the surface area, allowing more particles to come into contact and collide.
solution with a pH of 7 is described as this.
Neutral
Burning wood is an example of this type of change
type of change.What is a chemical change
A precipitate may be formed by mixing..
a. A liquid and another liquid
b. a Solid and a gas
c.a liquid and a solid
liquid and liquid
A candle is melted and then burned. Both processes involve the same candle. Explain why one is a physical change and the other is a chemical change.
Melting changes the state of the candle material without producing a new substance. Burning involves combustion, where the substances react and form new substances.
Why is burning petrol in a car considered a chemical change rather than simply a change in temperature?
The petrol reacts during combustion, producing new substances.
Heat is released as part of the chemical reaction.
Two identical reactions are performed. One is heated and the other is kept at room temperature. Predict which reaction will be faster and explain why.
The heated reaction will generally be faster because the particles have more kinetic energy and collide more frequently/energetically.
This is a substance with a pH less than 7.
What is an Acid
In this type of change, no new substance is formed
What is a physical change?
Which of the following always occurs during a chemical change?
a.change in colour
b.formation of a new substance
c.emision of light
d.all of the above
b. formation of a new substance
A chemical reaction produces bubbles. A student concludes that the bubbles prove a new substance has formed. Is their conclusion justified? Explain.
Not by itself. Bubbling can occur during a physical change such as boiling.
The student should look for additional evidence, particularly evidence that a new substance has formed.
Explain how chemical weathering can change a rock without simply breaking it into smaller pieces.
Chemical weathering involves chemical reactions that alter the substances in the rock, producing new substances.
What would you predict happens to the rate of a reaction if the concentration of a reactant is increased? Explain using particle collisions.
The reaction should become faster because there are more reactant particles in the same volume, increasing the frequency of collisions.
This is a substance with a pH greater than 7.
What is a Base?
In this type of change, new substances with different properties are formed.
What is a chemical change?
Why is a particle diagram useful when explaining a chemical reaction?
It can show that the particles in the reactants are rearranged to form different combinations of particles in the products.
A metal gate is left outside for several years and begins to rust. Why is rusting considered a chemical change?
The metal reacts with substances in its environment, producing new substances such as rust.
Rusting is a form of corrosion.
What chenical process allows cells to release energy from food?
Respiration
What is an Enzym and give one example.
Enzymes are biological catalysts that speed up chemical reactions in living things.
ex.Lipase
These positively charged particles are responsible for the acidic properties of a solution.
What are hydrogen ions (H⁺)?
Explain why melting ice and burning paper are different types of change.
Melting ice is physical because the substance remains water; burning paper is chemical because new substances are produced.
In the word equation
magnesium + hydrochloric acid → magnesium chloride + hydrogen
identify the reactants and products.
Reactants: magnesium and hydrochloric acid. Products: magnesium chloride and hydrogen
Photosynthesis and respiration are both chemical changes.
Why are they important to living things?
Photosynthesis produces glucose and stores energy as chemical energy, while respiration releases energy from food for cells to use.
Word equation for rusting.
iron + oxygen + water → hydrated iron oxide (rust)
what is a catalyst and explain how it speeds up a reaction
A catalyst is a substance that speeds up a chemical reaction without being used up or becoming a product of the reaction.
A catalyst provides an easier pathway for the reaction to occur.
When an acid reacts with a base, this type of reaction occurs, producing salt and water.
What is neutralisation?