Chemical reactions Flashcards
Chemical reactions make new ___.
chemicals
Atoms are __ during a chemical reaction, but the number of atoms does not change.
rearranged
Evidence of chemical reactions includes a large __ change, ___ , or a __ change.
temperature
bubbles
colour
Chemical reactions can be represented using.
equations
Do you think it would be easy to get the ingredients back after cooking? Explain your reasoning in terms of a chemical reaction.
It would be impossible to get the ingredients back from the cooked cake. This is because a chemical reaction has taken place between ingredients such as flour, baking powder, sugar, eggs and butter.
A new ___ must be produced for a chemical reaction to take place.
substance
Boiling is a ___ change, not a chemical reaction.
physical
There is a colour change when you add a teabag to a mug of boiling water. Why is this not a chemical reaction?
The chemicals in the tea are dissolving in the water, and dissolving is not a chemical reaction – it is a physical change.
Sodium bicarbonate is also known as __
baking soda.
__ is the chemical name for vinegar.
Ethanoic acid
If you mix ___ and __ , a reaction will occur, where lots of bubbles of carbon dioxide gas form.
vinegar
baking soda
whats the word formula for the reaction of vinegar and baking soda?
sodium bicarbonate + ethanoic acid → sodium ethanoate + water + carbon dioxide
Can you recall the formula for water and carbon dioxide?
The formula for water is H₂O. The formula for carbon dioxide is CO₂.
Physical changes, such as __ , __ and ____, do not make new chemicals. They are usually easy to __ .
melting
boiling
dissolving
reverse
In a chemical reaction, ___ between atoms are broken and made, so the atoms get ___ into new substances.
chemical bonds
rearranged
The simplest kind of chemical reactions involve two ___ reacting together to make a ___ .
elements
compound
Which two elements react together to make the compound sulfur dioxide?
Sulfur and oxygen.
A ___ is a chemical compound containing the element sulfur.
sulfide
What has happened to the total number of atoms during the chemical reactions?
They do not change.
When a chemical reaction happens, ___ is transferred to or from the surroundings.
energy
When energy is transferred to the surroundings, this is called an ___ reaction and usually feels hot.
exothermic
When energy is taken in from the surroundings, this is called an ___ reaction and usually feel cold
endothermic
In a ___ reaction, fuel is burned and reacts with __ to release energy.
combustion
oxygen
___ is the chemical change that takes place inside living cells. Glucose and oxygen are used to release energy that organisms need to live.
Respiration
Reactions that release energy (2)
- combustion
- respiration
Reactions that absorb energy (1)
- photosynthesis
___ absorbs energy from sunlight, allowing plants to make glucose and oxygen from carbon dioxide and water.
Photosynthesis
What happens to the temperature when citric acid and bicarbonate of soda were mixed?
The temperature decreases. We call this an endothermic reaction.
___ are chemical reactions which release energy from the chemicals into the surroundings.
Exothermic reactions
This energy is usually released as heat, so the surroundings get hotter.
Exothermic reactions don’t always release heat, sometimes the energy is released as ___ .
light
Is respiration an exothermic reaction or an endothermic reaction?
Respiration is an exothermic reaction because it releases energy.
What happens when Sodium hydroxide solution is poured into a beaker of hydrochloric acid.
The beaker now contains sodium chloride and water. The temperature on the thermometer has risen, meaning it is an exothermic reaction.
Thermal decomposition reactions are___ because they absorb energy when the chemicals are heated.
endothermic
What happens when sodium carbonate powder is tipped into a beaker of ethanoic acid.
The beaker now contains sodium ethanoate, water and carbon dioxide. The temperature on the thermometer has fallen, meaning it is an endothermic reaction.
When ammonium chloride powder is mixed with barium hydroxide powder and stirred, a chemical reaction takes place. The temperature drops to –14°C.
Is this reaction exothermic or endothermic?
It’s an endothermic reaction.
This is because the temperature of the surroundings decreased.
Exothermic and endothermic reactions that occur at room temperature in the science lab can be investigated using a ___ .
thermometer
How can I increase accuracy when measuring exothermic and endothermic reactions?
Accuracy can be improved by getting a precise value for the room temperature before the experiment begins, and using an insulated polystyrene cup to stop unwanted heat transfers.
Sometimes one result from a set of repeat measurements is very different from the rest of the results. This is called an __ or an ___ result.
outlier
anomalous
Why would it be a good idea to put an insulating lid onto the polystyrene cup when doing this experiment?
It would prevent heat from escaping out of the cup during an exothermic reaction and it would prevent heat from entering the cup in an endothermic reaction.
This makes the results more accurate.
A word equation represents a chemical reaction using the __ of the substances involved. Word equations do not show any __ or __ .
names
chemical symbols
formulae
In a chemical reaction, __ are the substances that react together, and ___ are the substances formed.
reactants
products
__ always take the form, reactants → products. A + sign separates two or more reactants or products.
Word equations
Which of the following processes is easier to reverse or undo?
Melting an ice cube
Burning a piece of wood
Melting and freezing are physical changes, so they are easy to reverse. To reverse this process the water needs to be cooled until it freezes again, probably using a freezer.
It is impossible to reverse the process of burning a piece of wood. This is because it is a chemical reaction.
Summarise the following chemical reaction into a word equation. Sulfuric acid reacts with black powdered copper oxide to make a solution of copper sulfate and water.
Sulfuric acid + copper oxide → copper sulfate + water
Reactants always go first in word equations, and the names of the reactants are separated using __ symbols.
+
In word equations, after the reactants, there is an __ , to show that the chemical reaction has taken place.
arrow, →
In word equations, The __ are written after the arrow, separated by + symbols.
products
When writing chemcial equations, never mix__ and ___ in the same equation.
words
formulas
Words like __ , ___ or __ , are not included in word equations.
powder
solution
gas
Can you spot the three mistakes in this word equation for the reaction taking place in a Bunsen burner?
Methane gas + oxygen = carbon dioxide plus water
The word gas should not be included.
The = symbol should be an arrow → instead.
The word plus should be swapped for a + symbol.
The correct equation is:
methane + oxygen → carbon dioxide + water
The chemicals which react together in a chemical reaction are called ___ .
reactants
A chemical reaction stops when one of the __ but there might be some of the other reactant left over.
reactants runs out,
Chemical reactions are normally __, unlike physical changes which can be reversed.
impossible to reverse
And when the wood in a fire has completely burnt, the burning __, even though there is plenty of oxygen present in the air.
stops
Can you name some differences between a physical change and a chemical reaction?
- Physical changes like melting and dissolving are usually easy to reverse, but chemical reactions are usually impossible to undo.
- Chemical reactions often involve a large energy change, bubbles, or a colour change as new chemical reactions are made.
In a chemical reaction, the ___ are the substances which are formed.
products
When the methane reacts with oxygen in a Bunsen burner, the products are usually __ and.
carbon dioxide
water
When hydrogen reacts with oxygen, water is made. What are the names of the reactants and products in this reaction?
The reactants are hydrogen and oxygen. There is only one product, water.
Here is the word equation for this reaction:
Hydrogen + oxygen → water
___ are a quick way of representing chemical reactions. They show us what atoms are involved and how they are bonded together.
Symbol equations
Symbol equations always take the form, ___ . A + sign separates two or more reactants or products.
reactants → products
__ are used in symbol equations to show whether each chemical is a solid, liquid, gas or solution.
State symbols
In a symbol equation, what symbol is used to show a chemical reaction has taken place?
An arrow → is used.
This goes between the reactants on the left and the products on the right.
In symbol equations, __ and are used to represent elements and compounds,
Chemical symbols
formulae
H₂ is the formula of __
hydrogen
H₂SO₄ is the formula of __
sulfuric acid
Mg is the symbol of magnesium, this is a symbol and not a formula because there are no __
numbers
Some __ elements are made from molecules. For example, hydrogen has a chemical formula of H₂, and oxygen is O₂. The little numbers are called ___ and show how many atoms of that element are present.
non-metal
subscripts
The formula of ammonia is NH₃. How many nitrogen (N) and hydrogen (H) atoms are present in the molecule?
Each ammonia molecule contains one atom of nitrogen and three atoms of hydrogen.
We know this because the hydrogen symbol has a subscript three after it, whereas the nitrogen symbol has no number meaning there’s only one.
The formulae of the__ always go first in a symbol equation. The __ are separated using a + symbol.
reactants
reactants
In a symbol equation, after the reactants, there is an __ to show that the chemical reaction has taken place.
arrow →
In a symbol equation, the __ are written after the arrow and are also separated by + symbols.
products
When carbon (C) is burned in air, the carbon reacts with oxygen (O₂) and __ is produced.
The symbol equation for this reaction is:
___
carbon dioxide (CO₂)
C + O₂ → CO₂
A symbol equation should only contain___ and __ for the chemicals.
Don’t use the names of the chemicals in a symbol equation.
symbols
formulae
What is the Law of Conservation of Mass?
During chemical reactions or a change of state, no atoms are created or destroyed. The total mass of chemicals before and after a reaction remains the same.
During chemical reactions or a change of state, no __ are created or destroyed. The total mass of chemicals before and after a reaction ___ .
atoms
remains the same
If you add 10 grams of sugar to 200 grams of warm water and stir to make a sugar solution, what mass of solution will you have?
10 grams of sugar plus 200 grams of water equals a total of 210 grams. Although you cannot see the dissolved sugar, all of the sugar particles and water particles you started with are still there.
Is the mass of the frozen water more than, less than, or the same as the mass of the liquid water?
The mass was the same in both. There was exactly the same number of atoms in the bottle. No atoms were created or destroyed, so the mass of the water/ice stayed the same.
Whenever a ___ or __ happens, the mass of the chemicals before is the same as the mass of the chemicals after. This is called the Law of Conservation of Mass.
physical change
chemical reaction
If a piece of wood is burned, the mass of the log and oxygen used in the burning will be __ as the mass of the gases produced and the remaining ashes.
the same
Mass is the measurement of the amount of matter and is measured in __ .
grams
The weight of an object is the gravitational force between the object and the Earth. Weight is measured in ___ .
newtons
The weight of an object depends upon its __ and ___ . The mass of an object stays the same wherever it is in the universe, but its weight can change.
mass
gravitational field strength
The weight of an object on the moon is __ of its weight on Earth.
1/6th
How much carbon is needed to produce 88 g of carbon dioxide, if 64 g is oxygen?
88 g - 64 g = 24 g
If 100 grams of water is put into a pan and boiled. Eventually, all the water will boil away as steam. If you collected all the steam and measured its mass, it would be exactly __ .
100 grams
What happens to the mass of a candle as it burns?
The mass of the candle will decrease. When the wax burns, it produces gases, carbon dioxide and water vapour. These gases then escape into the surrounding air.
Combustion is another name for ___ .
burning
In a __ reaction, fuel is burned and reacts with oxygen to release energy.
combustion
What do petrol, natural gas, wood and coal have in common?
They are all fuels, which means that they can be burned to release energy.
What are the three parts of the fire triangle?
A fuel, oxygen and heat are needed for a fire. If one of these is removed, a fire will go out.
In a combustion reaction, a __ is heated and it reacts with oxygen.
fuel
When fuels burn in combustion reactions, they release useful __
thermal energy (heat).
What is the difference between combustion and burning?
Nothing! They mean the same thing. Combustion is the scientific word for burning.
An oxidation reaction is one where a substance reacts with oxygen and produces __ .
oxides
An oxide is a chemical compound that contains at least one __ atom and one other element in its chemical formula.
oxygen
Combustion is an example of an __ reaction.
oxidation
Many fuels contain __ and __ atoms. These fuels burn to produce oxides, carbon dioxide and water.
carbon
hydrogen
H₂O, is __ .(name)
dihydrogen monoxide
Carbon dioxide, CO₂, is a __ that causes global warming.
greenhouse gas
Petrol is a fuel which is used in cars. Petrol is made from molecules which contain only carbon and hydrogen atoms. What is produced when petrol burns in a car engine?
Carbon dioxide (CO₂) and water (H₂O) which are both oxides.
What safety precautions would you take to protect yourself when investigating combustion reactions?
- Wearing safety goggles
- Wearing protective gloves
- Wearing a protective lab coat.
- Tying back hair and tucking away loose clothing, such as ties.
These precautions will help reduce the risk of injury from the combustion investigation like getting burnt.
The fuel used in gas barbeques is butane. Butane molecules contain only __ atoms and __ atoms and it is written as C₄H₁₀.
carbon
hydrogen
The word equation for the combustion of butane is, __
butane + oxygen → carbon dioxide + water.
The symbol equation for the combustion of butane is, __
C₄H₁₀ + O₂ → CO₂ + H₂O
Like all combustion reactions, __ will always be one of the reactants and be on the left of the equation.
oxygen
Most combustion reactions produce __ and __ , so these chemicals are written as the products on the right of the equation.
carbon dioxide
water
Charcoal is a fuel that contains carbon atoms but no hydrogen atoms. What is the word equation for the combustion reaction which occurs in a charcoal barbeque?
Carbon + oxygen → carbon dioxide
__ is the formula for methane.
CH₄
Methane reacts with oxygen in a combustion reaction. What is the product?
The product of the reaction is carbon dioxide (CO₂) and water (H₂O).
Thermal means__ . Decomposing is the process of __ .
heat
breaking down
What is thermal decomposition?
Thermal decomposition is a chemical reaction that happens when a compound breaks down when heated.
Baking powder and self-raising flour contain the chemical sodium hydrogencarbonate. This chemical breaks down when heated. What is released that makes cakes rise?
When sodium hydrogencarbonate is heated in the oven, it breaks down and releases carbon dioxide gas, making the cake rise.
What are the products when sodium hydrogencarbonate thermally decomposes?
Sodium carbonate, water and carbon dioxide.
Thermal decomposition reactions happen at __ . The reactants absorb lots of energy before breaking down into the products.
high temperatures
Thermal decomposition are examples of ___ reactions
endothermic
In a thermal decomposition reaction, there is only one __ , but two or more __.
reactant
products
When copper carbonate is heated, it breaks down to produce __ and __ .
copper oxide
carbon dioxide
Copper carbonate is green and copper oxide is black. You can see a colour change from __ to during the reaction.
green
black
Carbon dioxide produced can be detected using __ , which turns from __ to __
limewater
clear
cloudy
Word equation when copper carbonate is heated:
copper carbonate → copper oxide + carbon dioxide
Symbol equation when copper carbonate is heated:
CuCO₃(s) → CuO(s) + CO₂(g)
When magnesium carbonate is heated, it breaks down to produce __ and __ .
magnesium oxide
carbon dioxide
Magnesium carbonate and magnesium oxide are __ solids. (colour)
white
Word equation for heating magnesium carbonate:
magnesium carbonate → magnesium oxide + carbon dioxide
Symbol equation for heating magnesium carbonate:
MgCO₃(s) → MgO(s) + CO₂(g)
A state symbol is a symbol used in chemical equations to show if a substance is a __ , a __ , a __ , or an __ .
solid (s)
liquid (l)
gas (g)
aqueous solution (aq)
What is produced when calcium carbonate is heated?
Calcium oxide and carbon dioxide.
The word displace means __ .
to push out
A more __ element can displace a less __ element out of its compound during a chemical reaction.
reactive
reactive
Displacement reactions can be used to investigate the __ of metals and extract metals from __ .
reactivity
metal oxides
In a solution containing copper compounds, what metal can be used to extract copper?
Iron can be dipped into a solution of copper compounds to produce valuable metallic copper.
A chemical is described as being __ if it takes part easily and quickly in chemical reactions.
reactive
Metals can be arranged in order of their reactivity. This is called a ___ .
reactivity series
__ metals take part more slowly in chemical reactions or don’t react at all.
Unreactive
__ reactions involve a metal and the compound of a different metal.
Displacement
A more reactive metal will __ a less reactive metal from its compound in a __ reaction.
displace
displacement
After a displacement reaction the less reactive metal is left __ after the reaction.
uncombined
It is no longer chemically bonded to any other elements. It is now a pure element.
Magnesium is more reactive than copper. When a piece of magnesium is dipped into blue copper sulfate solution, a __ reaction occurs.
displacement
When a piece of magnesium is dipped into blue copper sulfate solution, the magnesium displaces the copper, and the products are __ and a solution of __ .
copper
magnesium sulfate
Word equation when magnesium reacts with copper sulfate:
magnesium + copper sulfate → copper + magnesium sulfate
Symbol equation when magnesium reacts with copper sulfate:
Mg(s) + CuSO₄(aq) → Cu(s) + MgSO₄(aq)
Can a reaction of magnesium with copper sulfate be reversed?
This reaction cannot happen in reverse. Copper cannot displace magnesium from a compound because copper is less reactive than magnesium.
Can copper displace magnesium from magnesium chloride solution?
No, copper is less reactive than magnesium. Only a more reactive metal will displace a less reactive metal from its compound.
When observing displacement reactions look for a __ change or change in __ . Record any observations in a results table, using words instead of numbers with units.
colour
temperature
Displacement reactions can be used to extract metals from their __ .
oxides
Carbon more reactive than some metals, such as copper, iron and lead. This means that some metals can be extracted from their __ using carbon.
metal oxides
Word equation for extracting copper from copper oxide using carbon:
copper oxide + carbon → copper + carbon dioxide
Write an equation to show how carbon can be used to displace lead from lead oxide.
lead oxide + carbon → lead + carbon dioxide
Chlorine, bromine and iodine all react in similar ways. Chlorine is the most reactive and iodine is the least reactive. In these non-metals:
- __ can displace __ and __ from their compounds.
- __ can dsiplace ___ but not __
- __ cannot displace __ or __
- Chlorine, bromine, iodine
- Bromine, iodine, chlorine
- Iodine, chlorine, chlorine
What reaction occurs when chlorine is added to a solution of sodium bromide?
chlorine + sodium bromide → bromine + sodium chloride
What reaction occurs if bromine is added to solution of sodium iodide?
bromine + sodium iodide → iodine + sodium bromid
Rank chlorine, iodone, and bromine from most reactive to least reactive
chlorine
bromine
iodine
What happens when iodine is added to a solution of sodium chloride?
No reaction.
Iodine is not reactive enough to replace those elemens.
If bromine is added to a solution of sodium chloride. What will happen?
No displacement reaction will occur because the bromine is less reactive than the chlorine.
In an oxidation reaction, a substance___ oxygen atoms.
gains
__ (burning) is an example of an oxidation reaction.
Combustion
What gas is needed for a fuel to burn?
Oxygen.
This is normally from the air but can also be from a specific source. For example, oxygen tanks are used for some space rocket engines.
Why does the mass increase after the iron oxide is burned?
The extra mass came from the oxygen atoms which bonded to the iron atoms.
Oxidation reactions occur when a substance reacts with the element oxygen to produce an __ .
oxide
Rusting is example of an __ reaction.
oxidation
Iron reacts with oxygen in the air and produces __ . __ is the scientific name for rust!
iron oxide
Iron oxide
Which element is involved in all oxidation reactions?
Oxygen.
The word equation for rusting is:
Iron + oxygen → iron oxide
Oxidation reactions involve a substance reacting with oxygen, which produces an oxide. This means they have oxygen as one of their __ , and an oxide as a __ .
reactants
product
magnesium and oxygen in the air react to produce __ .
magnesium oxide
Symbol equation to burn methane:
CH₄(g) + O₂(g) → CO₂(g) + H₂O(l)
Word equation to burn methane:
Methane + oxygen → carbon dioxide + water
Magnesium reacts with oxygen, resulting in __ as it burns.
a very bright light
