{"id":2117,"date":"2016-04-13T03:16:47","date_gmt":"2016-04-13T03:16:47","guid":{"rendered":"http:\/\/fisicaevestibular.com.br\/novo\/?page_id=2117"},"modified":"2024-08-21T14:54:53","modified_gmt":"2024-08-21T14:54:53","slug":"primeiro-principio-da-termodinamica-ou-principio-da-conservacao-da-energia","status":"publish","type":"page","link":"https:\/\/fisicaevestibular.com.br\/novo\/fisica-termica\/termodinamica\/primeiro-principio-da-termodinamica-ou-principio-da-conservacao-da-energia\/","title":{"rendered":"Primeiro Princ\u00edpio da Termodin\u00e2mica ou Princ\u00edpio da Conserva\u00e7\u00e3o da Energia"},"content":{"rendered":"

Primeiro Princ\u00edpio da Termodin\u00e2mica ou Princ\u00edpio da Conserva\u00e7\u00e3o da Energia<\/b><\/span><\/span><\/span><\/p>\n

Energia interna de um g\u00e1s perfeito<\/b><\/span><\/span><\/span><\/p>\n

A energia interna (U) de um g\u00e1s perfeito monoat\u00f4mico <\/b><\/span><\/span><\/span>corresponde <\/b><\/span><\/span><\/span>\u00e0 soma das energias cin\u00e9ticas m\u00e9dias (E<\/b><\/span><\/span><\/span>c<\/b><\/span><\/span><\/sub><\/span>) de todas as suas mol\u00e9culas e, pela lei de Joule \u00e9 fornecida por:<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

A energia interna de uma certa massa de um g\u00e1s perfeito \u00e9 fun\u00e7\u00e3o exclusiva da temperatura desse g\u00e1s<\/b><\/span><\/span><\/span><\/p>\n

\u00a0A <\/b><\/span><\/span><\/span>afirma\u00e7\u00e3o acima indica que a temperatura de um g\u00e1s<\/b><\/span><\/span><\/span> \u00e9 a <\/b><\/span><\/span><\/span>medida da energia cin\u00e9tica m\u00e9dia de suas mol\u00e9culas.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0Observe <\/b><\/span><\/span><\/span>nas figuras abaixo <\/b><\/span><\/span><\/span>que <\/b><\/span><\/span><\/span>quanto maior a temperatura maior \u00e9 o movimento vibrat\u00f3rio das <\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

mol\u00e9culas do g\u00e1s e<\/b><\/span><\/span><\/span>\u00a0consequentemente <\/b><\/span><\/span><\/span>maior a energia cin\u00e9tica (E<\/b><\/span><\/span><\/span>c<\/b><\/span><\/span><\/sub><\/span>) de suas mol\u00e9culas<\/b><\/span><\/span><\/span>, o que<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Como consequ\u00eancia da express\u00e3o acima, voc\u00ea deve observar que:<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0 <\/span>Aumento de temperatura\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>(\u0394T > 0) \u00a0\"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>aumento de energia inter<\/b><\/span><\/span><\/span>na\u00a0 \"\"\u00a0 <\/b><\/span><\/span><\/span>(\u0394U > 0).<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0<\/span>Diminui\u00e7\u00e3o de temperatura\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>(\u0394T < 0<\/b><\/span><\/span><\/span>)\u00a0 \"\"\u00a0 <\/b><\/span><\/span><\/span>diminui\u00e7\u00e3o de energia interna\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>(\u0394U<0).<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0<\/span>Temperatura constante\u00a0\"\" <\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>(\u0394T = 0)\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>energia interna constante\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>(\u0394U=0).<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

Primeiro Princ\u00edpio da Termodin\u00e2mica ou Princ\u00edpio da Conserva\u00e7\u00e3o da energia<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

O <\/b><\/span><\/span><\/span>Primeiro Princ\u00edpio da Termodin\u00e2mica (Princ\u00edpio da Conserva\u00e7\u00e3o da Energia) afirma que: <\/b><\/span><\/span><\/span>\u201cA energia n\u00e3o pode ser criada nem destru\u00edda, mas apenas transformada\u201d<\/b><\/span><\/span><\/span><\/p>\n

Exemplo num\u00e9rico:<\/b><\/span><\/span><\/span><\/p>\n

Suponha que um <\/b><\/span><\/span><\/span>sistema isolado receba Q = 300J de calor. <\/b><\/span><\/span><\/span>Se, <\/b><\/span><\/span><\/span>por exemplo<\/b><\/span><\/span><\/span>, \u0394U = <\/b><\/span><\/span><\/span>50J dessa energia forem absorvidos pelo sistema aumentando sua energia interna de 50 J, <\/b><\/span><\/span><\/span>ent\u00e3o a <\/b><\/span><\/span><\/span>parte restante, W = 250J, ser\u00e1 fornecida ao ambiente sob a forma de trabalho.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Ent\u00e3o, <\/b><\/span><\/span><\/span>Q = W + \u0394U ou,<\/b><\/span><\/span><\/span><\/p>\n

Estudo das transforma\u00e7\u00f5es gasosas baseado no primeiro princ\u00edpio da termodin\u00e2mica<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

Transforma\u00e7\u00e3o isot\u00e9rmica<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

Como a <\/b><\/span><\/span><\/span>temperatura (T) e a energia interna (U) de um sistema <\/b><\/span><\/span><\/span>est\u00e3o associadas \u00e0 <\/b><\/span><\/span><\/span>energia cin\u00e9tica das mol\u00e9culas, <\/b><\/span><\/span><\/span>se a <\/b><\/span><\/span><\/span>temperatura for constante (transforma\u00e7\u00e3o isot\u00e9rmica), a energia interna (U) do sistema tamb\u00e9m ser\u00e1 constante. <\/b><\/span><\/span><\/span><\/p>\n

Assim, a <\/b><\/span><\/span><\/span>varia\u00e7\u00e3o de energia interna (\u0394U) do sistema ser\u00e1 nula.<\/b><\/span><\/span><\/span><\/p>\n

Transforma\u00e7\u00e3o isot\u00e9rmica\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>\u0394U = 0 \"\"<\/b><\/span><\/span><\/span>\u00a0 \u0394U = Q \u2013 W\u00a0 \"\"\u00a0 0 = Q \u2013 W\u00a0 \"\"\u00a0\u00a0<\/b><\/span><\/span><\/span>Q = W.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Q = W<\/b><\/span><\/span><\/span> \"\" Portanto, numa <\/b><\/span><\/span><\/span>transforma\u00e7\u00e3o isot\u00e9rmica <\/b><\/span><\/span><\/span>(temperatura constante) <\/b><\/span><\/span><\/span>todo calor Q recebido pelo sistema \u00e9 totalmente transformado em trabalho.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0\"\"<\/span><\/p>\n

Transforma\u00e7\u00e3o isob\u00e1rica<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

Ocorre \u00e0 press\u00e3o constante. <\/b><\/span><\/span><\/span>A <\/b><\/span><\/span><\/span>varia\u00e7\u00e3o de temperatura (\u0394T) provoca uma varia\u00e7\u00e3o de energia interna (\u0394U) do sistema e a varia\u00e7\u00e3o de volume (\u0394V) produz trabalho.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

\"\"<\/p>\n

Parte<\/b><\/span><\/span><\/span> do calor (Q) recebido pelo sistema <\/b><\/span><\/span><\/span>\u00e9 <\/b><\/span><\/span><\/span>armazenada sob forma de energia interna <\/b><\/span><\/span><\/span>e parte<\/b><\/span><\/span><\/span> \u00e9 transformada em trabalho, de modo que \u0394U = Q \u2013 W.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\u00a0<\/span><\/p>\n

Transforma\u00e7\u00e3o isoc\u00f3rica, isom\u00e9trica ou isovolum\u00e9trica<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

\u00a0Ocorre a <\/b><\/span><\/span><\/span>volume constante\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>V<\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/sub><\/span>= V\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 \u0394V = 0\u00a0 \"\"\u00a0 <\/b><\/span><\/span><\/span>W = P.\u0394V\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 W = P.0\u00a0 \"\"\u00a0 <\/b><\/span><\/span><\/span>W = 0\u00a0 \"\"<\/b><\/span><\/span><\/span> <\/b>\u0394U = Q \u2013 W \"\"<\/b><\/span><\/span><\/span> \u0394U = Q \u2013 0\u00a0 \"\"\u00a0 <\/b><\/span><\/span><\/span>\u0394U = Q<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Transforma\u00e7\u00e3o adiab\u00e1tica<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

\u00a0Nela, o <\/b><\/span><\/span><\/span>sistema n\u00e3o troca calor com o meio externo (Q = 0) e isso ocorre porque o g\u00e1s est\u00e1 termicamente isolado ou porque a transforma\u00e7\u00e3o \u00e9 muito r\u00e1pida de modo que qualquer troca de calor com possa ser considerada.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0Se Q = 0 \"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>\u0394U = Q \u2013 W\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 \u0394U = 0 \u2013 W\u00a0 \"\"\u00a0 <\/b><\/span><\/span><\/span>\u0394U = \u2013 W.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\u00a0<\/span>Leia atentamente as informa\u00e7\u00f5es a seguir oas aplica\u00e7\u00f5es pr\u00e1ticas de algumas transforma\u00e7\u00f5es adiab\u00e1ticas<\/b><\/span><\/span><\/span>: <\/b><\/span><\/span><\/span><\/p>\n

Na <\/b><\/span><\/span><\/span>figura da esquerda abaixo<\/b><\/span><\/span><\/span>, ao <\/b><\/span><\/span><\/span>levantar o pist\u00e3o da bomba de bicicleta,<\/b><\/span><\/span><\/span> voc\u00ea <\/b><\/span><\/span><\/span>diminui a press\u00e3o interna o que faz abrir uma v\u00e1lvula localizada abaixo do pist\u00e3o, <\/b><\/span><\/span><\/span>fazendo o <\/b><\/span><\/span><\/span>ar externo penetrar no cilindro. <\/b><\/span><\/span><\/span><\/p>\n

Ao empurrar <\/b><\/span><\/span><\/span>o pist\u00e3o para baixo o aumento de press\u00e3o interna fecha automaticamente a v\u00e1lvula de entrada e abre a v\u00e1lvula de sa\u00edda ligada ao pneu for\u00e7ando o ar a penetrar no mesmo<\/b><\/span><\/span><\/span>. <\/b><\/span><\/span><\/span>Ao levantar o pist\u00e3o novamente voc\u00ea come\u00e7a tudo novamente.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\u00a0Observe que, <\/b><\/span><\/span><\/span>cada vez que voc\u00ea bombeia o ar no pneu, a bomba se aquece mais, <\/b><\/span><\/span><\/span>o que ocorre principalmente porque <\/b><\/span><\/span><\/span>voc\u00ea est\u00e1 for\u00e7ando as mol\u00e9culas de ar ficar mais pr\u00f3ximas umas das outras<\/b><\/span><\/span><\/span>, fazendo com que esse <\/b><\/span><\/span><\/span>trabalho de compress\u00e3o do g\u00e1s (negativo) aumente a energia interna (\u0394U), aumentando consequentemente a temperatura do g\u00e1s. <\/b><\/span><\/span><\/span><\/p>\n

Isso ocorre porque essa <\/b><\/span><\/span><\/span>transforma\u00e7\u00e3o \u00e9 adiab\u00e1tica (n\u00e3o troca calor com o ambiente, pois \u00e9 muito r\u00e1pida) e obedece \u00e0 fun\u00e7\u00e3o \u0394U= – W.<\/b><\/span><\/span><\/span><\/p>\n

Na <\/b><\/span><\/span><\/span>figura da direita (acima), <\/b><\/span><\/span><\/span>trata-se de uma <\/b><\/span><\/span><\/span>expans\u00e3o adiab\u00e1tica<\/b><\/span><\/span><\/span> <\/b>(muito r\u00e1pida e sem troca de calor com o meio ambiente), onde Q = 0 e \u0394U = Q \u2013 W\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 \u0394U = 0 \u2013 W\u00a0 \"\"\u00a0\u00a0\u0394U = \u2013 W\u00a0 \"\"\u00a0 o <\/b><\/span><\/span><\/span>volume do g\u00e1s aumenta (trabalho positivo) fazendo com que a energia interna (\u0394U) fique negativa e diminua, diminuindo assim, a press\u00e3o e a temperatura e a press\u00e3o, e o g\u00e1s resfria.\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

Transforma\u00e7\u00e3o c\u00edclica<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

\u00a0Consiste numa <\/b><\/span><\/span><\/span>s\u00e9rie de transforma\u00e7\u00f5es gasosas na qual o estado inicial coincide com o estado final, com o g\u00e1s retornando \u00e0 mesma press\u00e3o, volume e temperatura iniciais.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Toda transforma\u00e7\u00e3o c\u00edclica deve obedecer \u00e0s seguintes condi\u00e7\u00f5es:<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0Como <\/b><\/span><\/span><\/span>as temperaturas final e inicial s\u00e3o coincidentes (T<\/b><\/span><\/span><\/span>i <\/b><\/span><\/span><\/sub><\/span>= T<\/b><\/span><\/span><\/span>f<\/b><\/span><\/span><\/sub><\/span>), <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>varia\u00e7\u00e3o de energia interna (\u0394U) <\/b><\/span><\/span><\/span>\u00e9 <\/b><\/span><\/span><\/span>nula\u00a0<\/b><\/span><\/span><\/span> \"\"\u00a0\u00a0<\/b><\/span><\/span><\/span>\u0394U = 0<\/b><\/span><\/span><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0<\/span>\u0394U = Q \u2013 W\u00a0\"\"<\/b><\/span><\/span><\/span>\u00a0 0 = Q \u2013 W\u00a0 \"\"\u00a0 <\/b><\/span><\/span><\/span>Q<\/b><\/span><\/span><\/span>ciclo <\/b><\/span><\/span><\/sub><\/span>= W<\/b><\/span><\/span><\/span>ciclo<\/b><\/span><\/span><\/sub><\/span>\u00a0(a quantidade de calor trocada com o meio externo \u00e9 igual ao trabalho realizado na transforma\u00e7\u00e3o)<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0Em <\/b><\/span><\/span><\/span>toda transforma\u00e7\u00e3o c\u00edclica <\/b><\/span><\/span><\/span>representada no <\/b><\/span><\/span><\/span>diagrama PxV, o trabalho realizado <\/b><\/span><\/span><\/span>\u00e9 <\/b><\/span><\/span><\/span>fornecido pela \u00e1rea do ciclo.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0Se o <\/b><\/span><\/span><\/span>ciclo \u00e9 realizado no sentido hor\u00e1rio, o trabalho \u00e9 positivo.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\" Se o <\/b><\/span><\/span><\/span>ciclo \u00e9 realizado no sentido anti-hor\u00e1rio, o trabalho \u00e9 negativo.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

O que voc\u00ea deve saber, informa\u00e7\u00f5es e dicas<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Se a <\/b><\/span><\/span><\/span>temperatura \u00e9 a mesma para gases diferentes, <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>energia cin\u00e9tica das mol\u00e9culas deve ser a mesma, independente da massa de cada g\u00e1s.<\/b><\/span><\/span><\/span><\/p>\n

Como <\/b><\/span><\/span><\/span>E<\/b><\/span><\/span><\/span>c <\/b><\/span><\/span><\/sub><\/span>=mV<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\/2 e a energia cin\u00e9tica \u00e9 a mesma o g\u00e1s de maior massa deve ter menor velocidade para que essas energias se igualem.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

A<\/b><\/span><\/span><\/span> press\u00e3o exercida por um g\u00e1s \u00e9 o resultado das colis\u00f5es das mol\u00e9culas do g\u00e1s contra as paredes do recipiente e com a freq\u00fc\u00eancia e a intensidade das colis\u00f5es entre elas mesmas.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Os <\/b><\/span><\/span><\/span>gases ideais n\u00e3o existem<\/b><\/span><\/span><\/span>, pois s\u00e3o apenas <\/b><\/span><\/span><\/span>modelos te\u00f3ricos em que o volume das mol\u00e9culas e suas intera\u00e7\u00f5es s\u00e3o considerados desprez\u00edveis.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

O <\/b><\/span><\/span><\/span>Primeiro Princ\u00edpio da Termodin\u00e2mica (Princ\u00edpio da Conserva\u00e7\u00e3o da Energia) afirma que: <\/b><\/span><\/span><\/span>\u201cA energia n\u00e3o pode ser criada nem destru\u00edda, mas apenas transformada\u201d<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

\"\"\u00a0<\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

\u00a0Leia na teoria, procurando memorizar as aplica\u00e7\u00f5es pr\u00e1ticas sobre transforma\u00e7\u00f5es adiab\u00e1ticas.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Toda transforma\u00e7\u00e3o c\u00edclica deve obedecer \u00e0s seguintes condi\u00e7\u00f5es:<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0Como <\/b><\/span><\/span><\/span>as temperaturas final e inicial s\u00e3o coincidentes (T<\/b><\/span><\/span><\/span>i <\/b><\/span><\/span><\/sub><\/span>= T<\/b><\/span><\/span><\/span>f<\/b><\/span><\/span><\/sub><\/span>), <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>varia\u00e7\u00e3o de energia interna (\u0394U) <\/b><\/span><\/span><\/span>\u00e9 <\/b><\/span><\/span><\/span>nula\u00a0<\/b><\/span><\/span><\/span> \"\"\u00a0\u00a0<\/b><\/span><\/span><\/span>\u0394U = 0<\/b><\/span><\/span><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0<\/span>\u0394U = Q \u2013 W\u00a0\"\"<\/b><\/span><\/span><\/span>\u00a0 0 = Q \u2013 W\u00a0 \"\"\u00a0 <\/b><\/span><\/span><\/span>Q<\/b><\/span><\/span><\/span>ciclo <\/b><\/span><\/span><\/sub><\/span>= W<\/b><\/span><\/span><\/span>ciclo<\/b><\/span><\/span><\/sub><\/span>\u00a0(a quantidade de calor trocada com o meio externo \u00e9 igual ao trabalho realizado na transforma\u00e7\u00e3o)<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0Em <\/b><\/span><\/span><\/span>toda transforma\u00e7\u00e3o c\u00edclica <\/b><\/span><\/span><\/span>representada no <\/b><\/span><\/span><\/span>diagrama PxV, o trabalho realizado <\/b><\/span><\/span><\/span>\u00e9 <\/b><\/span><\/span><\/span>fornecido pela \u00e1rea do ciclo.<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0Se o <\/b><\/span><\/span><\/span>ciclo \u00e9 realizado no sentido hor\u00e1rio, o trabalho \u00e9 positivo.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\" Se o <\/b><\/span><\/span><\/span>ciclo \u00e9 realizado no sentido anti-hor\u00e1rio, o trabalho \u00e9 negativo.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

\"\"<\/p>\n

Cotidianamente s\u00e3o usados <\/b><\/span><\/span><\/span>recipientes de barro <\/b><\/span><\/span><\/span>(potes, quartinhas, filtros etc.) <\/b><\/span><\/span><\/span>para esfriar um pouco a \u00e1gua neles contida.<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Considere um <\/b><\/span><\/span><\/span>sistema <\/b><\/span><\/span><\/span>constitu\u00eddo por uma <\/b><\/span><\/span><\/span>quartinha cheia d’\u00e1gua.<\/b><\/span><\/span><\/span><\/p>\n

Parte da \u00e1gua que chega \u00e0 superf\u00edcie externa da quartinha,<\/b><\/span><\/span><\/span>\u00a0atrav\u00e9s de <\/b><\/span><\/span><\/span>seus poros, evapora, retirando calor do barro e da \u00e1gua que o permeia. <\/b><\/span><\/span><\/span><\/p>\n

Isso implica que tamb\u00e9m a <\/b><\/span><\/span><\/span>temperatura da \u00e1gua que est\u00e1 em seu interior diminui nesse processo.<\/b><\/span><\/span><\/span><\/p>\n

Tal processo se <\/b><\/span><\/span><\/span>explica<\/b><\/span><\/span><\/span> porque, na <\/b><\/span><\/span><\/span>\u00e1gua que evapora, s\u00e3o as mol\u00e9culas de \u00e1gua com maior energia cin\u00e9tica m\u00e9dia que escapam do l\u00edquido, diminuindo,<\/b><\/span><\/span><\/span> assim, a <\/b><\/span><\/span><\/span>energia cin\u00e9tica m\u00e9dia (relacionada \u00e0 temperatura) desse sistema.<\/b><\/span><\/span><\/span><\/p>\n

Assim, q<\/b><\/span><\/span><\/span>uanto <\/b><\/span><\/span><\/span>maior a velocidade de agita\u00e7\u00e3o das mol\u00e9culas, elas escapar\u00e3o com maior facilidade.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Durante a <\/b><\/span><\/span><\/span>compress\u00e3o de um sistema gasoso<\/b><\/span><\/span><\/span>, sob a <\/b><\/span><\/span><\/span>a\u00e7\u00e3o de uma for\u00e7a constante<\/b><\/span><\/span><\/span>, o <\/b><\/span><\/span><\/span>trabalho<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

realizado sobre o g\u00e1s \u00e9 negativo, <\/b><\/span><\/span><\/span>pois, se a <\/b><\/span><\/span><\/span>for\u00e7a \u00e9 constante a press\u00e3o ser\u00e1 tamb\u00e9m constante (isob\u00e1rica), com\u00a0<\/b><\/span><\/span><\/span>W=P.(V<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>\u00a0\u2013 V<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>).<\/b><\/span><\/span><\/span><\/p>\n

Como o g\u00e1s est\u00e1 <\/b><\/span><\/span><\/span>sendo comprimido \"\" V<\/b><\/span><\/span><\/span>2 <\/b><\/span><\/span><\/sub><\/span>< V<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\u00a0\"\" W < 0.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Mantendo uma <\/b><\/span><\/span><\/span>estreita abertura em sua boca, assopre <\/b><\/span><\/span><\/span>com vigor sua <\/b><\/span><\/span><\/span>m\u00e3o agora! <\/b><\/span><\/span><\/span>Viu? Voc\u00ea <\/b><\/span><\/span><\/span>produziu uma transforma\u00e7\u00e3o adiab\u00e1tica! Nela, o ar que voc\u00ea expeliu sofreu uma violenta expans\u00e3o, durante a qual o trabalho realizado correspondeu \u00e0 diminui\u00e7\u00e3o da energia interna desse ar (diminuindo sua temperatura), por n\u00e3o ocorrer troca de calor com o meio externo.<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Portanto, trata-se de uma <\/b><\/span><\/span><\/span>expans\u00e3o adiab\u00e1tica <\/b><\/span><\/span><\/span>(muito r\u00e1pida e sem troca de calor com o meio ambiente), onde <\/b><\/span><\/span><\/span>Q = 0 e \u0394U= Q \u2013 <\/b><\/span><\/span><\/span>W\u00a0 \"\"\u00a0 \u0394U= 0 \u2013 W \"\" <\/b><\/span><\/span><\/span>\u0394U = \u2013 W <\/b><\/span><\/span><\/span>\u00a0\"\"<\/b><\/span><\/span><\/span> \u00a0 o <\/b><\/span><\/span><\/span>volume do g\u00e1s aumenta (trabalho positivo<\/b><\/span><\/span><\/span>) fazendo com que <\/b><\/span><\/span><\/span>a energia interna (\u0394U) fique negativa e diminua, diminuindo assim<\/b><\/span><\/span><\/span>, a press\u00e3o e a <\/b><\/span><\/span><\/span>temperatura<\/b><\/span><\/span><\/span> \"\"\u00a0 o <\/b><\/span><\/span><\/span>g\u00e1s resfria<\/b><\/span><\/span><\/span>.\u00a0<\/b><\/span><\/span><\/span><\/p>\n

 <\/p>\n

Confira os exerc\u00edcios com resolu\u00e7\u00e3o comentada<\/span><\/a><\/h3>\n","protected":false},"excerpt":{"rendered":"

Primeiro Princ\u00edpio da Termodin\u00e2mica ou Princ\u00edpio da Conserva\u00e7\u00e3o da Energia Energia interna de um g\u00e1s perfeito A energia interna (U) de um g\u00e1s perfeito monoat\u00f4mico corresponde \u00e0 soma das energias cin\u00e9ticas m\u00e9dias (Ec) de todas as suas mol\u00e9culas e, pela lei de Joule \u00e9 fornecida por: A energia interna de uma certa massa de um g\u00e1s perfeito \u00e9 fun\u00e7\u00e3o exclusiva<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":2067,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"class_list":["post-2117","page","type-page","status-publish","hentry"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2117","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/comments?post=2117"}],"version-history":[{"count":2,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2117\/revisions"}],"predecessor-version":[{"id":2125,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2117\/revisions\/2125"}],"up":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2067"}],"wp:attachment":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/media?parent=2117"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}