chemistry yr 9 Flashcards
(27 cards)
What is the definition of exothermic reactions?
Reactions that release heat to the surroundings.
What is the result of an exothermic reaction?
The surroundings get hotter.
What is the energy flow in exothermic reactions?
Energy exits the system.
Give three examples of exothermic reactions.
- Combustion (burning wood, petrol, or gas)
- Fireworks (release heat, light, and sound)
- Condensation of steam (gas to liquid releases heat)
What is the definition of endothermic reactions?
Reactions that absorb heat from the surroundings.
What is the result of an endothermic reaction?
The surroundings get cooler.
What is the energy flow in endothermic reactions?
Energy enters the system.
Give three examples of endothermic reactions.
- Photosynthesis (plants absorb sunlight to make glucose)
- Cooking an egg (heat is absorbed to change its structure)
- Melting ice (solid absorbs heat to become liquid)
What is the quick tip to remember the difference between exothermic and endothermic reactions?
Exo = Exit (heat goes out), Endo = In (heat goes in).
What are the characteristics of acids?
- Taste: Sour
- pH Level: Less than 7
- Feel: Corrosive, not slippery
- Reacts with: Metals to produce hydrogen gas
- Turns litmus paper: Red
- Ion Released in Water: H⁺ (hydrogen ion)
What are some examples of acids?
- Hydrochloric acid (HCl)
- Citric acid
- Sulfuric acid (H₂SO₄)
What are the characteristics of bases?
- Taste: Bitter
- pH Level: Greater than 7
- Feel: Slippery or soapy
- Reacts with: Oils and fats
- Turns litmus paper: Blue
- Ion Released in Water: OH⁻ (hydroxide ion)
What are some examples of bases?
- Sodium hydroxide (NaOH)
- Ammonia (NH₃)
- Calcium hydroxide (Ca(OH)₂)
What is a neutralization reaction?
When an acid and base react together, they form salt + water.
What is the definition of combustion?
A chemical reaction where a substance reacts with oxygen to release heat and light.
What is the general formula for combustion?
Fuel + Oxygen → Carbon dioxide + Water + Energy (heat/light)
List five everyday uses of combustion.
- Cooking Food
- Transportation
- Heating Homes
- Electricity Generation
- Fireworks
What is the importance of balancing chemical equations?
To ensure the number of atoms of each element is the same on both sides of the reaction.
What is the Law of Conservation of Mass?
Matter cannot be created or destroyed in a chemical reaction.
What is pH?
A scale that measures how acidic or basic (alkaline) a substance is.
What are the pH scale ranges?
0–6 = Acidic, 7 = Neutral, 8–14 = Basic/Alkaline.
What does pH stand for?
Potential of Hydrogen.
How can we test pH?
- Litmus paper
- Universal indicator
- pH meter
What effect does combustion have on coal?
It results in the oxidation of carbon and hydrogen, producing carbon dioxide, water, and heat.
