{"id":2043,"date":"2016-03-08T00:44:30","date_gmt":"2016-03-08T00:44:30","guid":{"rendered":"http:\/\/fisicaevestibular.com.br\/novo\/?page_id=2043"},"modified":"2024-08-21T14:30:19","modified_gmt":"2024-08-21T14:30:19","slug":"calor-latente-trocas-de-calor-com-mudanca-de-estado","status":"publish","type":"page","link":"https:\/\/fisicaevestibular.com.br\/novo\/fisica-termica\/calorimetria\/calor-latente-trocas-de-calor-com-mudanca-de-estado\/","title":{"rendered":"Calor Latente \u2013 Trocas de calor com mudan\u00e7a de estado"},"content":{"rendered":"

Calor Latente \u2013 Trocas de calor com mudan\u00e7a de estado<\/b><\/span><\/span><\/span><\/p>\n

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

Calor Latente<\/b><\/span><\/span><\/span><\/p>\n

O <\/b><\/span><\/span><\/span>calor recebido por um corpo pode fazer com que sua temperatura aumente <\/b><\/span><\/span><\/span>ou que ele <\/b><\/span><\/span><\/span>sofra uma<\/b><\/span><\/span><\/span> <\/b>mudan\u00e7a de estado<\/b><\/span><\/span><\/span>. <\/b><\/span><\/span><\/span>No segundo caso voc\u00ea tem uma <\/b><\/span><\/span><\/span>quantidade de calor latente<\/b><\/span><\/span><\/span>,\u00a0ou seja, o <\/b><\/span><\/span><\/span>calor<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

latente se refere \u00e0 quantidade de calor que um corpo recebe <\/b><\/span><\/span><\/span>apenas para mudar de estado, o que ocorre \u00e0 temperatura constante.<\/b><\/span><\/span><\/span><\/p>\n

Constata-se que a <\/b><\/span><\/span><\/span>quantidade de calor latente (Q) cedida ou retirada de uma subst\u00e2ncia para que ela <\/b><\/span><\/span><\/span>mude de estado o que sempre ocorre \u00e0 <\/b><\/span><\/span><\/span>temperatura constante <\/b><\/span><\/span><\/span>\u00e9 <\/b><\/span><\/span><\/span>diretamente proporcional \u00e0 sua massa (m), e depende das caracter\u00edsticas da subst\u00e2ncia (L). <\/b><\/span><\/span><\/span>Matematicamente:<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

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

Significado de Calor Latente<\/b><\/span><\/span><\/span><\/p>\n

Se voc\u00ea quiser saber, por exemplo, <\/b><\/span><\/span><\/span>quantas calorias s\u00e3o necess\u00e1rias <\/b><\/span><\/span><\/span>para <\/b><\/span><\/span><\/span>fundir 200g de alum\u00ednio<\/b><\/span><\/span><\/span>, voc\u00ea deve fazer\u00a0 \"\"\u00a0 <\/b><\/span><\/span><\/span>Q = m.L = 200.94\u00a0 \"\"\u00a0Q = 18.800 cal ou Q = 18,8 kcal.<\/b><\/span><\/span><\/span><\/p>\n

Curva de aquecimento – calor sens\u00edvel e calor latente<\/b><\/span><\/span><\/span><\/p>\n

Observe <\/b><\/span><\/span><\/span>com muita aten\u00e7\u00e3o o <\/b><\/span><\/span><\/span>gr\u00e1fico abaixo <\/b><\/span><\/span><\/span>e a <\/b><\/span><\/span><\/span>sequ\u00eancia de figuras <\/b><\/span><\/span><\/span>que ilustra o aquecimento, por exemplo, de certa massa de \u00e1gua sendo aquecida de <\/b><\/span><\/span><\/span>gelo a -20<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C at\u00e9 vapor de \u00e1gua a 120<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C.<\/b><\/span><\/span><\/span><\/p>\n

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

\"\"<\/p>\n

\"\"<\/p>\n

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

\"\"<\/p>\n

\"\"<\/p>\n

Durante a <\/b><\/span><\/span><\/span>fus\u00e3o e a vaporiza\u00e7\u00e3o a temperatura permanece constante <\/b><\/span><\/span><\/span>(0<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C na fus\u00e3o e 100<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C na<\/b><\/span><\/span><\/span><\/p>\n

vaporiza\u00e7\u00e3o) porque a <\/b><\/span><\/span><\/span>energia t\u00e9rmica (calor) fornecida ao gelo foi utilizada apenas para convert\u00ea-lo em \u00e1gua l\u00edquida <\/b><\/span><\/span><\/span>e a <\/b><\/span><\/span><\/span>energia t\u00e9rmica (calor) fornecida \u00e0 \u00e1gua l\u00edquida foi utilizada apenas para convert\u00ea-la em vapor<\/b><\/span><\/span><\/span>, fazendo com que a <\/b><\/span><\/span><\/span>temperatura nessas duas mudan\u00e7as de estado f\u00edsico permane\u00e7a constante (0<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C na fus\u00e3o e 100<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C na vaporiza\u00e7\u00e3o).<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Quando <\/b><\/span><\/span><\/span>voc\u00ea afirma que o calor latente de fus\u00e3o do gelo \u00e9 de 80 cal\/g<\/b><\/span><\/span><\/span>, voc\u00ea quer dizer que, <\/b><\/span><\/span><\/span>para a fus\u00e3o de 1g de gelo ou para a solidifica\u00e7\u00e3o de 1g de \u00e1gua, voc\u00ea deve ceder ou retirar 80 cal.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Curva de aquecimento \u2013 calor sens\u00edvel e calor latente<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Mudan\u00e7as de estado f\u00edsico<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Resolvendo<\/b><\/span><\/span><\/span> alguns exerc\u00edcios <\/b><\/span><\/span><\/span>sobre trocas de calor envolvendo <\/b><\/span><\/span><\/span>calor sens\u00edvel (espec\u00edfico) e calor latente:<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Dados: <\/b><\/span><\/span><\/span>calor espec\u00edfico\u00a0do\u00a0gelo = 0,5 cal\/g\u00b0C<\/b><\/span><\/span><\/span>; <\/b><\/span><\/span><\/span>calor\u00a0espec\u00edfico\u00a0da\u00a0 \u00e1gua\u00a0 = 1 cal\/g\u00b0C <\/b><\/span><\/span><\/span>e <\/b><\/span><\/span><\/span>calor\u00a0 latente\u00a0 de\u00a0 fus\u00e3o\u00a0 do\u00a0 gelo\u00a0 = 80 cal\/g<\/b><\/span><\/span><\/span><\/p>\n

Resolu\u00e7\u00e3o:<\/b><\/span><\/span><\/span><\/p>\n

De <\/b><\/span><\/span><\/span>gelo a -20<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C a gelo a 0<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 n\u00e3o tem mudan\u00e7a de estado \"\" <\/b><\/span><\/span><\/span>calor sens\u00edvel\u00a0 \"\" <\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>Q<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span> = m.c<\/b><\/span><\/span><\/span>gelo<\/b><\/span><\/span><\/sub><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

\u2206\u03b8 <\/b><\/span><\/span><\/span>= 2.0,5.[0 \u2013 (-20)]\u00a0 \"\"\u00a0 <\/b><\/span><\/span><\/span>Q<\/b><\/span><\/span><\/span>1 <\/b><\/span><\/span><\/sub><\/span>= 20kcal\u00a0 (calor utilizado no aquecimento do gelo).<\/b><\/span><\/span><\/span><\/p>\n

De <\/b><\/span><\/span><\/span>gelo a 0<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C a \u00e1gua a 0<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C\u00a0 \"\" <\/b><\/span><\/span><\/span>\u00e9 uma mudan\u00e7a de estado (fus\u00e3o) \u00e0 temperatura constante \"\"\u00a0 <\/b><\/span><\/span><\/span>calor latente de fus\u00e3o \u00a0\"\" <\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>Q<\/b><\/span><\/span><\/span>2 <\/b><\/span><\/span><\/sub><\/span>= m.L <\/b><\/span><\/span><\/span>= 2.80\u00a0 \"\"\u00a0 <\/b><\/span><\/span><\/span>Q<\/b><\/span><\/span><\/span>2 <\/b><\/span><\/span><\/sub><\/span>= 160 kcal\u00a0(calor utilizado apenas na mudan\u00e7a de estado). <\/b><\/span><\/span><\/span><\/p>\n

De <\/b><\/span><\/span><\/span>\u00e1gua a 0<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C a \u00e1gua a 50<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 n\u00e3o tem mudan\u00e7a de estado \"\" <\/b><\/span><\/span><\/span>calor sens\u00edvel\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>Q<\/b><\/span><\/span><\/span>3 <\/b><\/span><\/span><\/sub><\/span>= m.c<\/b><\/span><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub><\/span>. \u2206\u03b8 <\/b><\/span><\/span><\/span>= 2.1.(50 \u2013 0)\u00a0 \"\"\u00a0 <\/b><\/span><\/span><\/span>Q<\/b><\/span><\/span><\/span>3 <\/b><\/span><\/span><\/sub><\/span>= 100 kcal\u00a0 (calor utilizado no aquecimento da \u00e1gua at\u00e9 a temperatura pedida, 50<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C).<\/b><\/span><\/span><\/span><\/p>\n

A quantidade de calor total nesse aquecimento foi <\/b><\/span><\/span><\/span> <\/b>Q<\/b><\/span><\/span><\/span>total<\/b><\/span><\/span><\/sub><\/span> <\/b>= 20 + 160 + 100 = <\/b><\/span><\/span><\/span>280 kcal.<\/b><\/span><\/span><\/span><\/p>\n

Como a <\/b><\/span><\/span><\/span>fonte t\u00e9rmica fornece 20 kcal por minuto\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 \u0394t = \"\"<\/b><\/span><\/span><\/span>= 14minx60 = 840 s.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Num <\/b><\/span><\/span><\/span>piquenique,<\/b><\/span><\/span><\/span> com a finalidade de se <\/b><\/span><\/span><\/span>obter \u00e1gua gelada, <\/b><\/span><\/span><\/span>misturou-se num <\/b><\/span><\/span><\/span>garraf\u00e3o t\u00e9rmico<\/b><\/span><\/span><\/span>, de<\/b><\/span><\/span><\/span>\"\"<\/p>\n

capacidade t\u00e9rmica desprez\u00edvel, <\/b><\/span><\/span><\/span>2kg de gelo picado a 0\u00b0C e 3kg de \u00e1gua que estavam em garrafas ao ar livre, \u00e0 temperatura ambiente de 40<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0Desprezando-se a troca de calor com o meio externo e <\/b><\/span><\/span><\/span>conhecidos o calor latente de fus\u00e3o do gelo (80 cal\/g) <\/b><\/span><\/span><\/span>e o <\/b><\/span><\/span><\/span>calor espec\u00edfico da \u00e1gua (1 cal\/g\u00b0C).<\/b><\/span><\/span><\/span><\/p>\n

Calcule <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>massa de \u00e1gua gelada dispon\u00edvel para se beber, em kg, <\/b><\/span><\/span><\/span>depois<\/b><\/span><\/span><\/span> de\u00a0estabelecido o equil\u00edbrio t\u00e9rmico<\/b><\/span><\/span><\/span><\/p>\n

Resolu\u00e7\u00e3o:<\/b><\/span><\/span><\/span><\/p>\n

Calor necess\u00e1rio <\/b><\/span><\/span><\/span>para <\/b><\/span><\/span><\/span>fundir os 2 kg de gelo a 0 \u00b0C\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>Q<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span> = m.L <\/b><\/span><\/span><\/span>= 2000.80 <\/b><\/span><\/span><\/span>= 160000 cal\u00a0(calor utilizado para derreter os 2 kg de gelo).<\/b><\/span><\/span><\/span><\/p>\n

Calor necess\u00e1rio para resfriar os 3 kg de \u00e1gua de 40<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C at\u00e9 0 \u00b0C\u00a0<\/b><\/span><\/span><\/span> \"\"\u00a0 <\/b><\/span><\/span><\/span>Q = m.c.\u0394\u03b8 <\/b><\/span><\/span><\/span>= 3000.1.(0-40) <\/b><\/span><\/span><\/span>= <\/b><\/span><\/span><\/span><\/p>\n

– 120000 cal (calor retirado dos 3 kg de para passar de 40<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C at\u00e9 0<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C. <\/b><\/span><\/span><\/span><\/p>\n

Observe<\/b><\/span><\/span><\/span> que o <\/b><\/span><\/span><\/span>calor liberado pela \u00e1gua, 120 kcal<\/b><\/span><\/span><\/span>, <\/b><\/span><\/span><\/span>n\u00e3o \u00e9 suficiente para fundir todo gelo <\/b><\/span><\/span><\/span>(visto que <\/b><\/span><\/span><\/span>s\u00e3o necess\u00e1rios 160 kcal<\/b><\/span><\/span><\/span>)\u00a0 \"\"\u00a0 portanto o <\/b><\/span><\/span><\/span>equil\u00edbrio t\u00e9rmico ocorrer\u00e1 a 0 \u00b0C<\/b><\/span><\/span><\/span>, sendo que <\/b><\/span><\/span><\/span>os 3 kg de \u00e1gua l\u00edquida original continuar\u00e1 l\u00edquida <\/b><\/span><\/span><\/span>e teremos <\/b><\/span><\/span><\/span>uma parte do gelo derretida que vale\u00a0 \"\"<\/b><\/span><\/span><\/span> \u00a0 <\/b><\/span><\/span><\/span>Q = m.L\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 120000 = m.80\u00a0 \"\"\u00a0 \u00a0m = \"\" <\/b><\/span><\/span><\/span>= 1500 g = 1,5 kg.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0Assim a <\/b><\/span><\/span><\/span>massa de \u00e1gua gelada <\/b><\/span><\/span><\/span>final ser\u00e1 de <\/b><\/span><\/span><\/span>3 kg <\/b><\/span><\/span><\/span>(l\u00edquido j\u00e1 existente a 0<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>C) + <\/b><\/span><\/span><\/span>1,5 kg <\/b><\/span><\/span><\/span>(gelo que derreteu<\/b><\/span><\/span><\/span>) = <\/b><\/span><\/span><\/span>4,5 kg.<\/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":"

Calor Latente \u2013 Trocas de calor com mudan\u00e7a de estado \u00a0 Calor Latente O calor recebido por um corpo pode fazer com que sua temperatura aumente ou que ele sofra uma mudan\u00e7a de estado. No segundo caso voc\u00ea tem uma quantidade de calor latente,\u00a0ou seja, o calor latente se refere \u00e0 quantidade de calor que um corpo recebe apenas para<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":2030,"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-2043","page","type-page","status-publish","hentry"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2043","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=2043"}],"version-history":[{"count":2,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2043\/revisions"}],"predecessor-version":[{"id":2051,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2043\/revisions\/2051"}],"up":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2030"}],"wp:attachment":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/media?parent=2043"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}