8F Reactions Flashcards
State two observations that a chemical reaction is occurring.
Temperature change, colour change, fizzing, smell, irreversible change
Describe what an exothermic reaction is.
A reaction which released thermal energy
Give one example of an exothermic reaction.
Combustion/burning, metal and acid, neutralisation/acid and alkali
What is a neutralisation reaction?
An acid reacts with an alkali
What happens in terms of energy when bonds are broken?
Energy is taken in
What happens in terms of energy when bonds are made?
Energy is given out
True or false: During an exothermic reaction, products have more energy than reactants.
How can we measure whether there is a temperature change during a reaction?
Thermometer
What happens when bonds in reactants are broken?
Energy is absorbed
What happens when bonds in products are made?
Energy is released
What are the reactants in an instant cold pack?
Water and ammonium nitrate
How does the instant cold pack work?
water and ammonium nitrate react in an endothermic reaction
Identify the independent variable during this investigation.
Mass of ammonium nitrate
Identify the dependent variable during this investigation.
Temperature change
Identify the control variables during this investigation.
Volume of water, the balance reading zero before use
How do you calculate the temperature change?
By finding the difference between the before and after temperature
What is a catalyst?
A substance that can be added to a chemical reaction to speed it up
Why are catalysts described as “specific”?
A catalyst which works for one reaction, will not work for another reaction
How do catalysts speed up reactions?
By lowering the activation energy
What is an enzyme?
A biological catalyst
Give an example of a reaction which is sped up by an enzyme
Digestion, respiration, photosynthesis
What is the name of the part of the enzyme which has a specific shape?
Active site
Which catalyst is used to manufacture ammonia?
Iron or platinum
Give one reason why industrial processes use catalysts
More product made in a shorter time, enzymes can be re-used, lower energy costs during production
What are the two reactants of combustion?
Fuel and oxygen
In addition to the reactants, what else is needed for combustion?
Heat
What are the products of combustion?
Carbon dioxide and water
What is a fuel?
A material that burns to release energy
Define hydrocarbon.
A compound containing only hydrogen and carbon
What is complete combustion?
When a fuel burns in excess oxygen
What is incomplete combustion?
When a fuel burns in a limited supply of oxygen
What are the products of incomplete combustion?
Carbon monoxide, soot, water
What are the three sides of the fire triangle?
Heat, fuel, oxygen
How can we extinguish any fire?
By removing one side of the fire triangle
Which side of the fire triangle is removed by water?
Heat
Why can’t water be used to extinguish an electrical fire?
It will cause electrocution
How does a carbon dioxide fire extinguisher put out a fire?
CO2 is more dense than air so sinks and prevents oxygen getting to the fire
If not extinguished, why do most fires eventually go out?
The fuel runs out
What is a fire blanket?
A heavy blanket which prevents oxygen getting to the fire
What are two uses of fire blankets?
When a person’s clothing is on fire, chip pan fires
What is a fuel?
A material which burns to release energy
What is a fossil fuel?
A fuel made of dead plants and animals that died and were buried millions of years ago
Name the three fossil fuels.
Coal, oil, natural gas
State two uses of fuels.
To keep us warm, for transport, to generate electricity
In the fuel investigation, what is the independent variable?
Different fuels
In the fuel investigation, what is the dependent variable?
Mass of fuel burned
In the fuel investigation, identify two control variables.
Volume of water, increase in temperature
How do we calculate how much energy is needed for a 1°C temperature rise?
Divide the mass of fuels burned by the temperature change
What is thermal decomposition?
Substances are broken down by heat
Why are thermal decomposition and combustion not the same?
Combustion involves oxygen, thermal decomposition does not
What are the products of thermal decomposition of a metal carbonate?
Metal oxide and carbon dioxide
What are the products of thermal decomposition of magnesium carbonate?
Magnesium oxide and carbon dioxide
What makes a carbonate?
One carbon atom and three oxygen atoms
What solution is used to test for carbon dioxide?
Limewater
What is a positive test for the presence of carbon dioxide?
Limewater goes cloudy
Give one use of thermal decomposition.
To produce lime for glass, cement, and limewater, as the first step in extracting copper from its ore
What do we mean if we say that a metal carbonate is “thermally stable”?
Metal carbonates which will not break down when heated
Without doing an experiment, how can we decide whether a metal carbonate will be thermally stable?
Thermally stable metal carbonates usually contain more reactive metals
Why can’t all metal carbonates be thermally decomposed using a Bunsen burner?
Bunsen burner does not reach high enough temperatures
Which metal carbonate changes colour when it thermally decomposes?
Copper carbonate
Which metal oxide glows yellow when heated?
Zinc carbonate
How do we test for carbon dioxide?
Limewater
Write a word equation for the thermal decomposition of zinc carbonate.
Zinc carbonate 🡪 Zinc oxide + Carbon dioxide
How do we know that thermal decomposition is an endothermic reaction?
Heat energy is taken in during the reaction
Give an example of a physical change.
Ice melting, any change of state
Give an example of a chemical change.
Combustion
What is the law of conservation of mass?
Mass of the reactants equals the mass of the products, it cannot be lost or gained
Who described the law of conservation of mass?
Lavoisier
What seems to happen to the mass of a reaction if one of the reactants is a gas?
Increases
What seems to happen to the mass of a reaction if one of the products is a gas?
Decreases
Why should you not look directly at the magnesium ribbon during heating?
It burns with a bright white light
What is the purpose of the balloon over the neck of the conical flask?
To capture the gas produced
