C7 - chemical reactions Flashcards
What is an endothermic reaction?
A chemical reaction that absorbs energy in the form of heat from its surroundings and cools them.
e.g:
- Melting of ice-cubes
- A cold pack
- Photosynthesis: Plants absorb heat energy from sunlight to convert carbon dioxide and water into glucose and oxygen.
What is an exothermic reaction?
A chemical reaction that releases energy in the form of light or heat and heats its surroundings.
e.g:
- The making of an ice cube.
- A heat pack.
- Lighting matches.
- ^^ Combustion.
what are hydrocarbons?
A combustible compound.
e.g:
- Coal
- Petrol
- Natural gas -> methane gas, ethane > fossil fuels
- diesel
What are incomplete combustions?
A combustion reaction that occurs with less oxygen. Less oxygenated fires will make more carbon smoke, soot and burn cooler.
Methane + Oxygen → Carbon + Carbon monoxide + Water
CH(4) + O(2) → C + 2H(2)O
What is a combustion?
A large amount of energy released as heat. Normally it will make fire, but if the reaction happens very quickly it can create an explosion.
Fuel + Oxygen → Carbon Dioxide + Water
CH(4) + 2O(2) → CO(2) + 2H(2)O
What is the word equation for the combustion of Magnesium
Magnesium + Oxygen → Magnesium Oxide, an exothermic reaction.
What is the reactant necessary for every combustion reaction to occur?
Oxygen
What is the general equation for respiration?
C6H12O6 + 602—–>6H2O + 6C02
What is the general equation for photosynthesis?
6CO2 + 6H2O + light energy → C6H12O6 + 6O2
Define and determine properties of acids
A corrosive chemical substance, tastes sour and has a pH level of 8-14
Define and determine the properties of bases.
Bases have a bitter taste and feel slippery or soapy to touch. Some bases are very corrosive, like caustic soda (sodium hydroxide).
Define pH
The concentration of hydrogen ions in a solution on a scale.
Pink on the scale means it’s a… strong or weak, acid or base or neutral?
Pink on the scale is a strong acid
green on the scale means it’s a… strong or weak, acid or base or neutral?
Green on the scale is neutral
blue on the scale means it’s a… strong or weak, acid or base or neutral?
blue on the scale is a strong base.
pH scale (that measures how acidic or basic a substance is) ranges from…?
pH scale ranges from 1 (acidic) to 14 (basic)
If a substance has a pH of 7 what is it?
Neutral; a pH of 7 is neutral
Will a strong acid or base have a pH of 12?
base; pH’s above 7 are bases.
Will a strong acid have a high or low pH?
Lower; the smaller the number the more acidic.
Define neutralisation.
Neutralisation a reaction between an acid and a base. A salt and water (a neutral liquid) are the products of this type of reaction.
Define and determine properties of ions
An ion is an atom or group of atoms (a molecule) in which the number of electrons is different from the number of protons (negatively or positively charged).
What is an alkali?
An alkali is a base that can be dissolved in water and is the opposite of an Acid, and has a pH greater than 7. They often have a bitter taste and slimy mouthfeel.
All alkali are bases but all bases are not alkali.
Define a negative ion
A negatively charged ion.
Define a positive ion
A positively charged ion.
